It also makes his grumpiness a bit less of an outlier to consider him in that context. If you run into 60s/70s-era AI/Lisp-hacker types at AI conferences, they're usually pretty grumpy, but also quite intelligent, so they get away with their grumpiness and not-very-polite negative questions (often complete with Stallman-style interruption of people in the middle of a talk to correct some minor point).

(Not true of everyone, of course.)