The former is more implausible because Chinese people with that level of English are quite rare, whereas English people able to create a fake Chinese username are not.
I feel like you're making three statistical mistakes at once.
- First, we're not discussing the English level of the general Chinese population, but specifically of the group that's also good at programming. That conditional probability is much higher.
- Even if we did speak of the general Chinese population, that is a lot of people so something rare in that group is true for many people still!
- It's not like everyone in the US has great English either. (Though open source maintainers are again probably more likely to.)
And China has been enticing ethnic Chinese who grew up in the West to "come back to the Motherland" with promises of riches for a long time now. Quite a few made the switch, too. I very much doubt that finding a native English speaker is a problem if it's the PRC govt.
It does make it less likely to be Russia, though. Although of course this could always just be subcontracted.
- First, we're not discussing the English level of the general Chinese population, but specifically of the group that's also good at programming. That conditional probability is much higher.
- Even if we did speak of the general Chinese population, that is a lot of people so something rare in that group is true for many people still!
- It's not like everyone in the US has great English either. (Though open source maintainers are again probably more likely to.)