He was neither Dave nor JP. His name was either Clinton something or Cliff something - I didn't quite catch it. (Maybe it was Clinton Hammond; he's Canadian, isn't he?)
Thanks for your input everybody. I agree that this man wasn't breaching the local etiquette in playing with me unsolicited, since that's how it works there - I was just surprised because I haven't come across this kind of format before. But apparently it's not so unusual.
You're right, Jon Freeman, I should have gone one night just to listen before performing. I also discovered in the course of the night that almost all the acts were country or bluegrass stuff. So now I'll try to to choose material that might be remotely pleasing to country fans (finding a folkier venue is not easy in my current state of geographical/transportational isolation).
Yes Shambles, I'll be going back. I really enjoyed the ambience - it wasn't a bar, but rather a firehall set up with rows of chairs, with treats brought by participants shared during the intermission. The crowd seemed very nice; I was with a couple of my housemates who have learning disabilities (I live in a L'Arche home) and people were very welcoming to us and tolerant of their little-bit-different-from-normal behaviours.
And you know, I learned something important through this open mike and through this thread: I've often heard that "it's about the music, not the musicians" but it didn't really click with me what that meant till now. I had been thinking of doing a song called "War Bride's Waltz" (Aengus Finnan) not only for its moving lyrics but because I've been practicing a little guitar solo to go with it that I wanted to show off.
So at first I thought: there's no point in doing the War Bride's Waltz because if the other guys play the attention will be distracted from my guitar solo and I can't impress the audience with my skills. But now I realize that the thing to do is play the song, just with chords, and nod to the others to take the solo when it comes up. This way a great song will be presented to the audience in the better arrangement than I could have done on my own, and it doesn't matter who gets the glory.
This must sound like a moment from Chicken Soup for the Soul, but I really did just come to understand the concept that it's about the music, not the musician.
I don't think I'll do anymore a cappella stuff, just because it doesn't seem to fit the venue.
I mentioned being there with some men with mental disabilities; in fact when I was chatting with the MC and mentioned that they play guitar and fiddle, he said that they were welcome to perform too. I'll have to think long and hard about that one (they play very, very badly) but maybe once we've been there long enough... open means open, right?