Because the group in question isn't the majority group, and still isn't after this increase.
It's definitely eliding a lot of the nuance of the article, but technically it's not wrong.
And there is a shit ton of diversity in Mexico and across South America.
Population growth was about 3.45m, 3.15m of that was hispanic, 1.18m was asian, 0.6m was black, 0.6m was 2+ races, and white were -2.1m (yes negative). Numbers according to the article, as well as categories.