Ah, outdoor gigs, such fun. I played one in Connecticut on May 25th and it was 47 degrees (8?C) with sideways rain and wind gusts which made it feel like 40 (4?C). I was wearing a hooded jacket and when the wind would blow rain at us I'd turn my back to the audience. Nice stage presence, huh? HA!
Yes Jazzyvee, my guess is that a certain combination of temperature, humidity, and maybe dew point caused your sticky situation. It may be different for others but for me things feel best when it's dry. So I think your second idea - wiping the fingers (maybe the strings too) - was probably the right direction. Sometimes in between tunes you can hold your hand near an amp or stage light fan which is putting out warm dry air.
The only thing to do is ignore these distractions and concentrate on the music. Don't become obsessed trying to figure out what's happening or the music will suffer. Also know that the rest of the band is probably fighting the same battle!
Three cheers for indoor gigs!
Jimmy J