I think those who are maligning Charlie need to re-read his opening post. If "Open sessions" were promised, they weren't delivered, and if "keeping sessions going" was what the people were booked for (incidentally, I first read "twenty something" as referring to the number of them) then what they did was not the same, and making faces at others' performances (TDL excepted) is not polite or welcoming, and nicking someone's chair is distincly rude.

Not replying to conversation in sessions is a bit more debatable - many feel that conversation in sessions is rude, but a short politeness beteen tunes is surely appropriate.

Sessioning one's own tunes without including known tunes is not engaging: it limits participants to those who know those tunes and that seems not to have been what the payers were booked for. But there is a place for new tunes - they have to start somewhere.

It does look as if there may have been a crossed wire about the nature of the sessions - some non-singers interpret the expression as excluding singers whereas I would suggest that it should include them (but not if all they want to do is solo) so that accompanied song (with the accompaniment staying in keeping) is as much part of a session as joining in with the played tune of another (and again you should not walk all over it).

It is helpful to those joining in if modulations and variations are preceed by an indication of the new key, by the usual finger gestures if necessary.