After 10+ years here I can safely say that it’s not they are antisocial. But more weary.
As a culture they don’t talk to strangers and don’t like to be talked to by them either.
As for foreigners, they kind of avoid you if you don’t speak the language.
How I’m perceived and treated when I didn’t speak Japanese compared to today is a huge difference as most Japanese do not know how to communicate in English.