Your conclusion is that they were acting the way they were expected to - which is certainly possible. I'm not sure. But I don't think you considered another possibility, which is this night out was a release, and it was refreshing to go out and not think deep thoughts. Or, in other words, to go out and have fun.

Yes, when you're with good friends you know well, you can seamlessly go back and forth between serious conversation and fun, goofing around conversation. But when you're around new people, and you want to have a good time, I think we (as a species) tend towards goofing around conversation. If I've been working a lot, a night out where I don't think Deep Thoughts is exactly what I want.

And for the record, I tend not to go into too much detail about my work unless I'm seriously prodded because, really, what I do is boring to most people.

So, my point: there are alternate explanations.