Couldn't have thought of a better description

There are essentially two types of people in Mensa: those who think they're smarter than everyone else and decide to take a Mensa IQ test to prove it to everyone, and those who took an IQ test for some other reason and then decided to check what's all this Mensa thing about.

You don't need Mensa to meet some smart people, but it's an easy place to find them, for better or for worse (both of which can be interesting experiences, BTW).

I was in Mensa for a few years but wasn't getting much out of it so I dropped it. I would have dropped it sooner, but my mother liked doing the puzzles in the newsletter. I have had the good fortune to have smart friends and work with a lot of very smart people so I have never been starved for intellectual stimulation. But not everyone is so lucky, and it soon became clear to me from letters in the Mensa newsletter that it was a godsend to bright people living in small, rural communities who had no one around who understood them. We now have on-line communities that can provide similar companionship for isolated intelligent people, without having to join a formal society like Mensa.

When I looked (decade ago), your description would have characterized their online haunts but not IRL meetings.

Maybe being online turns anything into Reddit/HN.

On the other hand, word was most members are inactive and only a small percentage turn up at IRL events at all, i.e. strong (self) selection effects.

As far as I can tell, it's a boardgaming club. I only went to two or three meetings before lapsing, though.