Most likely, no: that number is not correct.
The article that you link to appears to be a re-published 1989 article by Canadian writer James Bacque. In the book Other Losses published in the same year, Bacque claims that hundreds of thousands of German prisoners died in Allied prisoner camps after WWII. However, in what has been called the '"Other Losses" Debate", many historians have refuted this claim, and their estimates for the number of causalities in these camps are two to three orders of magnitude smaller.
There is a rather detailed Wikipedia article on Bacque's book that summarizes his argument. Basically, he argues that it was food shortages, diseases and exposure to cold that caused hundreds of thousands in the Allied POW camps established after WW2 mostly on the left-hand side of the Rhine River, the so-called Rheinwiesenlager ("Rhine Meadow Camps").
Simplifying considerably, he bases his conclusions mostly on the available data on the size of the Wehrmacht in the West by the time of Germany's capitulation in 1945 and the number of prisoners published by US officials since since then. Bacque argues that there's a figure labelled "Other Losses" (hence the title of his book) in the "Monthly Reports of the Military Governor" of the US Zone in Germany that changes dramatically from ~800,000 in November to ~1,800,000 in December. He reads this as evidence for his claim of an immense death toll:
The victims undoubtedly number over 800,000, almost certainly over 900,000 and quite likely over a million. Their deaths were knowingly caused by army officers who had sufficient resources to keep the prisoners alive.
The Wikipedia article also contains a long "Criticism" section with a considerable number of references. The section starts with the conclusion of a 1990 symposium that reviewed the book. To quote:
The panel comments that, among its many problems, Other Losses
- misuses documents
- misreads documents
- ignores contrary evidence
- employs a statistical methodology that is hopelessly compromised
- made no attempt to see the evidence he has gathered in relation to the broader situation
- made no attempt to perform any comparative context
- puts words into the mouths of the subjects of his oral history
- ignores a readily available and absolutely critical source that decisively dealt with his central accusation
As a consequence of those and other shortcomings, the book "makes charges that are demonstrably absurd."
What is true, however, is that after WWII there were a massive 20 million missing persons right after the end of WWII (including both civilians as well as soldiers killed in action and prisoners of war), and even today, the fate of about one million of them is unknown (for a short overview, see this 2018 DW.com article). However, with regard to unaccounted German prisoners of war, all evidence appears to imply that they rather disappeared in Soviet camps than in camps run by the Western Allies – even though there is agreement that conditions were also poor in the Rhine Meadow Camps, but not so poor as to be responsible for deaths in the regions Bacque claims.
That's one of the main conclusions of a 1992 publication ("Die vermißte Million", unfortunately only available in German) by US historian Arthur L. Smith. Smith's book is, in some regards, a direct response to Bacque. While he agrees that poor conditions in the Rhine Meadow Camps led to a non-insignificant number of deaths among German prisoners, he vehemently opposes Bacque's claims (and calls them "ridiculous" in at least two places). In his conclusion, he summarizes what he considers to be irrefutable facts:
- Zwar ist als wahr anzuerkennen, daß in den Rheinwiesenlagern zwischen 8000 und 40000 (niederste und höchste Schätzung) deutsche Kriegsgefangene umgekommen sind, doch ist es gänzlich ausgeschlossen, daß dort eine Million Männer gestorben sein könnten, ohne die geringste Spur zu hinterlassen. […]
- Die gründliche Arbeit der diversen deutschen Suchdienste führte, wenn es um vermißte Soldaten ging, die zuletzt im Westen gewesen waren, in nahezu allen Fällen zur Identifizierung. […] Die Million Vermißter ist im Westen nicht zu ermitteln.
- Durch die ausgezeichnete Arbeit des Länderrats und des Zonenbeirats sowie ihrer Ausschüsse für Kriegsgefangenenfragen, die wiederum aufs engste mit dem Internationalen Roten Kreuz, dem YMCA und den Suchdiensten kooperierten, konnte schon früh festgestellt werden, daß die überwältigende Mehrheit der vermißten Wehrmachtsangehörigen im Osten verschwunden war; sie war dort entweder gefallen oder nach Kriegsende in sowjetischen Lagern umgekommen.
Translation (adapted from deepl.com):
- While it must be accepted as fact that between 8000 and 40000 (lowest and highest estimate) German prisoners of war perished in the Rhine Meadow Camps, it is entirely impossible that a million men could have died there without leaving a trace. [...]
- The thorough work of the various German tracing services with regard to soldiers who had last been in the West led to an identification in almost all cases. [...] The million missing soldiers cannot be located in the West.
- Through the excellent work of the Zonal Advisory Councils in Germany as well as their committees for prisoner-of-war issues, which in turn cooperated closely with the International Red Cross, the YMCA, and the tracing services, it was possible to determine early on that the overwhelming majority of missing Wehrmacht members had disappeared in the East; they had either fallen there or perished in Soviet camps after the end of the war.
The 1992 "Essay and Reflection: On the 'Other Losses' Debate" by S. P. MacKenzie reaches a similar conclusion that Bacque's book doesn't hold up to academic scrutiny:
The eventual consensus opinion in academic circles will doubtless be that Bacque's thesis, taken as a whole, rests on shaky foundations. But because much of what Bacque claims concerning camp conditions is beyond dispute, and because it is precisely these sections of the book which make the most emotionally compelling reading, it is unlikely, for good or ill, that Other Losses will fade quickly away in the public mind.
Turns out that this assessment was spot-on.