I think it's pretty logical, though perhaps it is correlation rather than causation.

Say I am hiring as a native English speaker in a Chinese company (while of course still knowing enough Mandarin to survive) and I have 3 candidates, one of whom also speaks English fluently. I would definitely be biased towards the English speaker, because I would work better with them.

Now, it doesn't really matter what their ethnicity was, but there is a higher likelihood of them being of the same ethnicity. Especially if my first language is niche, the chances of hiring the same ethnicity would be higher.

I've been on the receiving end of this before, being hired in part because I spoke English due to my manager while the rest of the company was primarily Mandarin