The C++ coding style is also very much the way a Windows developer would write C++ code. Not the way a Unix-y C++ developer writing on Windows would write.
I always figured based on the code and the emails that it was an older Japanese developer. I've emailed 100s of them over the years and they do all typically write similar in English, they mix a lot of UK/US-ism, and often their English is really good, like I wouldn't know they weren't a native English-speaker until I just caught on to how they wrote. (Speaking is an entirely different issue, many of them cannot speak English in person very well or make obvious grammatical mistakes they don't make when typing.)
I always figured based on the code and the emails that it was an older Japanese developer. I've emailed 100s of them over the years and they do all typically write similar in English, they mix a lot of UK/US-ism, and often their English is really good, like I wouldn't know they weren't a native English-speaker until I just caught on to how they wrote. (Speaking is an entirely different issue, many of them cannot speak English in person very well or make obvious grammatical mistakes they don't make when typing.)
Windows is also very pervasive among developers.