isn't Satoshi Japanese as well?
This is actually unlikely, it is more probable that he is European due to a very good knowledge of the English language, the usage of British English spellings, and a couple other things I can't recall at the moment but a Google would probably get you there.
That doesn't mean anything. There are millions of A+ Chinese students who write perfect British English online. I've done business & talked with plenty of them on forums. Their word usage, grammar and spelling is top notch.
You could never tell they are Chinese unless they used nicknames indicating their place of origin.
I don't see how that's any different for Japan or any other country. English is my 3rd language but I'm 100% fluent in it, maybe more so than in my native language which I've already forgotten partially.
I just had to put in my penny's worth....
One thing you can count on, if someone's English is excellent, they are probably not English