Lavanya Ramanathan is using a definition of "white" that is contrary to the US definition.
This can be seen by a more-complete quotation:
Immigration and birthrate trends suggest that by 2046, the United States will be made up of more non-whites than whites. And the change will be fueled in part by immigrants from Latin and South America, from Asia and Mideast nations, but also by their American-born children and grandchildren.
Oppositely, the United States defines white as:
White – A person having origins in any of the original peoples of Europe, the Middle East, or North Africa
The "Middle East" is defined in immigration law as ending at the Pakistan western border.
By self-report, in 2010, 26.7 million out of 50.5 million Hispanics considered themselves "white alone" and another 2.4 million consider themselves white in combination with another race.
The US definition of "Hispanic" is:
“Hispanic or Latino” refers to
a person of Cuban, Mexican,
Puerto Rican, South or Central
American, or other Spanish
culture or origin regardless of
A much more accurate article on this topic is the New York Times article The Myth of a White Minority which links to actual data and says:
In March , it projected that non-Hispanic whites would be a minority by 2044
The predictions make sense only if you accept the outdated, illogical methods used by the census, which define as a “minority” anyone who belongs to “any group other than non-Hispanic White alone.”
So Ramanathan should have said "less than 50% non-Hispanic white-alone persons" instead of "more non-whites than whites", used 2044 not 2046, and linked to a data source.