BBS meetups weren't really like that. You had young/old mismatched people who could communicate because life wasn't online back then.
Even people who had internet access back then used BBSs to communicate with people near them on topics that were either local or which generally interested them.
Most boards had spaces which allowed general discussion of anything, even if the BBS was created with a specific subject in mind (computers, warez, occult stuff, photography, etc).
Lots of the people I saw at meetups were a bit on the shy/awkward side, which wasn't too uncommon for people who were into computers in general those days, but they were able to get along fine at meetups because they already knew many (if not most) of the other people there. They'd spent hours talking, and debating, and sharing ideas with them. They could go to a meetup and talk about all the same things they talked about online and they already had some idea of how people would react to them.
A local BBS was a great place to meet friends because it gave people a safe space to get to know each other at their own pace with carefully chosen words before being forced into real-time face to face interaction, and once they already had relationships established the transition to hanging out in real life was made much easier.
Teenagers with nerdish interests (me and my crowd), hippie physicists from the local university, BDSM people, swingers (a lot of swingers, probably party people by nature), a few Hitler-was-right Nazis here and there, some pagan types, conspiracy theorists, gay & lesbian folks, and on and on. There was a some overlap in the crowds, and at the bashes everyone mixed and matched just fine. Fun was had by all.
I later dated someone from those bashes for a few years, and a couple of people from back then are good friends to this day. Still in touch with a few more, all of whom are doing interesting things.