I would say that Japanese are antisocial by nature, I mean Japan is famous for its hikikomori isn't it ?
A long time ago I was with a girl who has been in a travel agency in Japan, we were in Europe and went to a famous tourist spot,
she told me about a tour girl she knew who sometimes bring tourist to this spot, and it happens she just saw that girl there,
so I told to go and greet her, but she decline say the girl she did not want to disturb the girl during her work... weird..
I mean lot most of people from other countries they would see someone they know on a trip abroad, I think they would at least say hi.
I also have noticed that Japanese mothers with a child in baby car often they put the child face to the wall, maybe there are practical side to this but I would doubt a western woman would do that. I remember once I was on a train there were two Japanese mothers with babies, the babies start to see each other and interact, one of the mother expression less, took her baby and put him in another direction, maybe she feared the interactions between the babies would disturb the peace on the train, I don't know western woman would probably let the children do and smile at each others, don't think this is something you would see in Japan.
Not talking about those Japanese colleagues whom I never seen the face for years because they have been constantly wearing a mask for the past 5 years.
Not talking about that family of five (I think) next door whom me or my wife never seen outside for the past 5 years, I have a good view of their house, so that's quite a feat to go out unnoticed for years, no idea how they look like.