I have seen exclusively white people teams, especially at smaller startups. They were all Americans though, so not much diversity of nationalities.
Given that China and India are countries with 1.4B population, no surprise that one can find enough people to form exclusively Chinese (or Indian) teams. Another factor is that people from other backgrounds do not want to join such teams even if the hiring manager makes them an offer. When I was at a FAANG, my team composition slowly drifted towards only Chinese and Indian, as people from other backgrounds left in 6-12 months after an Indian manager came in.
I'm sure it happens at small companies, but at large companies I've never seen it. It wouldn't be allowed to stay that way if it did happen. The number of times I've seen it happen with Chinese and Indians teams, relative to how rare it is for white-only teams to exist, seems highly improbable. White people are the plurality if not majority at most big American tech companies, so if it's all just statistical noise it should happen more with white people and that just isn't what happens.
I have seen enough white-only teams while at FAANG. Those were not in SV but in smaller US cities. Of course that was rare but then again, chinese-only or indian-only teams were rare as well.
Given that China and India are countries with 1.4B population, no surprise that one can find enough people to form exclusively Chinese (or Indian) teams. Another factor is that people from other backgrounds do not want to join such teams even if the hiring manager makes them an offer. When I was at a FAANG, my team composition slowly drifted towards only Chinese and Indian, as people from other backgrounds left in 6-12 months after an Indian manager came in.