From what I've seen and read it regularly flags native English writing as AI too. Sometimes even changing a few words is enough for it to change the verdict.

It's not command of the english language it flags (for native vs non native to matter), it's stylistic mannerisms, some of which happen to also exist in some direct translation of some foreign patterns for some languages.

But it detects them in a crude manner, missing obvious AI slop, and misflagging human texts.