It still sounds chancy. Without some kind of compensation it's possible it went something like:
Host: "So can you and spouse make it?"
Band guy: "Sure, we wouldn't miss it!"
H: "Awesome, Rick and Mervis are gonna be there too, you guys should bring your gear and play some tunes!"
BG: "That sounds fun! What do you think, like two sets? We can bring a PA system, is the venue good with this?"
H: "oh yeah I'm sure it'll be fine, they have bands all the time, bring your guitar it'll be fun"
BG: "Sounds good!" *sets to work organizing everything*
H: *completely forgets about casual mention of playing songs, doesn't think about it again until BG contacts them two weeks before for more info about "gig"* **AWKWARD**