Well he may have been a pillock, but...

As I remarked, if he was trying to play with others without tuning to them, all the criticisms are justified. But if he was just preferring not to have them playing with him when he was singing a song or two, I can't see there's anything wrong with that. I've never known a session where that isn't perfectly acceptable behaviour.

It can be bloody distracting if people leap in with a backing when they don't necessarily understand the tune, or when you're still a bit shaky on how it goes yourself. Not being in tune might have seemed a more tactful way of achieving that than saying it right out, though clearly in this case it turned out not to be. Capoing up and playing in an impossible key is another way so far as some instruments are concerned.

And if he was pointing out that there's really no universal "concert pitch" and that traditional musicians are often nowhere near the pitch of electronic tuners, that's true enough.