Shambles - I was posting at same time as you, so my reference to control freaks is coincidental & not related to yours - just in case confusion ensues......

The CF to whom you refer was probably labouring under the delusion that he/she was being helpful encouraging and complimenting the poor embarrassed guy. I've seen similar happen a few times. It can be quite funny, so long as all the musicians see the funny side.
At a festival campsite recently someone gave feedback the next day on what they'd overheard of a bunch of people singing & playing. They pointed out who they thought was good & who was bad etc, and had completely missed the point that it had been a bunch of people enjoying themselves & that relative abilities hadn't been an issue.
- sort of related I think - but maybe a bit drifty, sorry.

Kris