Maybe the guitarist had too much happy juice, smoke or powder and lost the plot, hence the reprimand?
Still, no matter how much the guitarist was ruining the vibe and everyone's rep, the onstage slap made everything much worse. If I was playing with a guitarist floundering like that I'd try to help out and knit his phrases together as much as possible. It sure beats hanging him out to dry and stopping.
One time played I played in a scratch band at a big party where the singer imbibed too much beforehand and was worse than useless. Two of the band members were pros and one was so incensed he never spoke to the singer again afterwards. I have video footage of us playing the riff of Telegraph Sam for about several minutes with NOTHING happening! lol
In hindsight, as drummer, I maybe had some responsibility to lead everyone into a merciful end to the debacle, but as a lightweight in the group (not as light as the singer lol) I played it safe and stayed with the backbeat.
So everyone stayed put, looking at each other wondering what the hell to do and hoping the singer might get his stuff together - but he just mumbled the words from a lyric sheet and cracked bad jokes before it somehow ended. From memory he did okay in a Stooges song later on but too little too late.
I also played in the support band (keys), and that was obviously more functional. So the only time I ever "supported myself" I got upstaged