Historically, White meant European. It still often does. Everyone knows this, though some play the ‘white’ is pigmentation not ancestry game.
I came across an example of this game in a comment at Steve Sailer’s blog:
So maybe Steve or someone else can clarify something for me here. The current Hispanic population in America is 15%. But apparently, 2/3 of that, or 10% is actually Hispanic White. Aren’t Hispanic Whites basically, well, Whites? I mean is there any difference between a Hispanic White actor like Andy Garcia as opposed to say Tom Cruise?
The author asks why Steve distinguishes between White Ancestral Europeans and Hispanics. In reply, one might ask why the US government does. And why social institutions do likewise, for examples, when it comes to quotas.
I guess because they are interested in talking about differences and pinpointing their etiology. Given that the government is so interested, it sounds reasonable for everyone else to be likewise.
As for group and population differences, whether medical or social, there are a number of possible causes. Common endogenous factors include average genetics, group culture, etc.
Here are the population genetics of White European. The average fst (genetic distance) is .009, making White Continental European relatively homogeneous. In the US, White Ancestral Europeans are even more so.
Here are the population genetics of Hispanics.