My money is also on bigotry, but the way Dingus said “began to kiss” makes me wonder how intense it was. If he’d said “gave my partner a kiss” that’s one thing, but “began to kiss” sounds like it might have been more like “making out” which I don’t want to see anyone doing in a restaurant.
I’m just speculating and the real answer is probably homophobia, especially given the assault that ensued.