Really? Every form I've ever seen has had a separate check box for "Latino / Hispanic"...

I think often there's an option for race and then a separate option for Latino/Non-Latino. I would guess that most Latino people would probably be White and Latino, although its not something I'm super knowledgeable about.

Most people in the "Hispanic or Latino" group would also be in the "White" group, although there are not insignificant numbers of black or asian hispanics.

Also keep in mind that in official US usage that term basically means "someone from a Spanish cultural background OR a Latin American country". Although some agencies specifically exclude countries from Latin America without a Spanish or Portuguese culture.

So a white guy whose grandparents immigrated from Spain counts (the grandparents spoke Spanish), and a Quechua from Bolivia who recently immigrated and only speaks Runasimi counts (Bolivia has a Spanish culture), and a black guy from Guyana might count. The OMB says no (Guyana was colonised by the British), but the Census says yes (it's in South America, so close enough).

The system makes very little sense.

It's not uncommon. The 77% figure quoted in the top comment includes Hispanics ("White Hispanics"). The White non-Hispanic population is 62%.

Although to be fair, Asians constitute 15% of the population of California as a whole.