They certainly do not create more particulate emissions, but they might not create that much less than a gasoline powered car, depending on the model of car considered.
First, what was previously thought? According to point IV.a.55 of this report the council of Europe's standing committee on Science and Technology, electric vehicles produce no fine particulate emissions. The report is dated 1998 however, so things may have changed since.
The new study (perhaps
review' orarticle' would be better? It's a think tank's internal publication, not peer reviewed) can be read in full here (google translate did a pretty good job this time), but you need to look at the Dutch version for the graphs.
The very first section already answers our question. The author never claims that electric cars produce more particulate emissions than ordinary cars. The title of the section says it all: "Electric cars produce almost as much particulate matter (PM) [as] modern petrol or diesel cars".
The first graph in this section solidifies this. The electric cars considered all have lower total PM emissions than any of the similarly sized cars that are not EVs, though only modestly lower for the most part. A small gasoline car produces slightly less emissions than a medium sized EV however.
Figures 3 and 4 suggest that the reason the advantage is so small now is because tighter emissions standards have dramatically reduced PM from cars over the last 25 years. So when the council of Europe report was written, it probably was fair to say that electric vehicles had no PM emissions at all (as compared to existing gasoline powered cars), but this is apparently no longer true.
The last part of the section concerned with emissions seems very badly done to me, and at best is educated speculation. The author tries to mathematically compute an estimate for the increase in PM emissions from the extra weight of an electric car, but uses an unsourced formula with very nice round numbers, that I believe is likely to have been made up on the spot (33.33% factors for everything?). Even this slipshod analysis finds that the electric version of a normal family car is no worse than the gasoline version for PM emissions, and smaller EVs are much better.
On the whole, I think the news story ought to have been: "Emissions Standards so Good that Gasoline Cars Now Competitive with EVs!" which is still exciting, but doesn't mislead the reader into thinking this was always the case, or that it's an argument against EVs in and of itself (remember, EVs are unchanged at the level of PMs that Council of Europe considered to be zero. It's that gasoline powered cars have dropped by > 75% for gasoline, and even more for diesel since the report was written).