I am comparing people all over the world how I socialize with them from time to time. I see lots of people from all over the world are quite social, especially the West but Japanese don't go online quite often.
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.
Of course they are anti-social toward people who don't understand their language. Do you often talk to the foreigner(s) who can't speak a lick of your native language? LOL. I want to learn Japanese so bad just for the opportunity to talk to beautiful Japanese women. Same reason for learning any language from my perspective, it is increasing my chance of romance.