Maybe it's a myth, but it sure sounds plausible. The software that checks the "Windows 9" substring doesn't even have to exist for this to be reason they chose to skip to version 10 — they just had to be concerned that it might exist.
Sure, maybe there's no C function that returns the string, but there's a ver command. It would be trivial to shell out to the command. https://en.wikipedia.org/wiki/Ver_(command)
Doctor here, I'm sorry to inform you that you have a case of parasitic copyleftiosis. Your brain is copyleft, your body is copyleft, and even your future children will be copyleft.