I believe they are referring to Cluster B and C personality disorders.

https://en.wikipedia.org/wiki/Classification_of_personality_disorders

I got 2.7k on a post, but I just got lucky.

https://www.youtube.com/@TsodingDaily

If you’re a programmer, or think you might want to be one, I highly recommend this channel. He’s a savant at all sorts of low level things, quite funny and entertaining, and does a fantastic job of explaining what’s going on.

It’s not just a fat or muscle thing. Those both contribute of course; fat insulates and muscle produces more heat. But the real player is the surface area to volume ratio.

A bigger person has a lot more volume than they have a bigger surface area, and since heat is lost through the skin this has a major impact.