Depending on who you're talking with, that might not be exactly true. Honestly, I've seem flamewars that were on the levels of emacs vs. vim. So I actually found this to be one of the more belivable scenes. Quite in constrast to the Tor scene at the beginning.

Maybe the point was to make the scene awkward?

Now that would be unrealistic.

You can't really guess which distro someone is using just by glancing over their screen for a second.

You can tell which DE they are using but not distro, except in the case of Unity and Pantheon, those are mostly used with their respective distros. People don't usually have output of cat /etc/os-release on the screen easily visible for people passing by to see.

There isn't that much visible difference between distros if you aren't working as root.

FWIW I've basically had the conversation seen in the show, albeit with a friend, not a stranger. He was running XFCE because it was the default in Debian, and I was running KDE (have been for twelve years). So I found the exchange at least plausible. I think it boils down to the fact that, some people find DE quite uninteresting (unlike editors), while others have strong feelings about them.