Superman is a good guy, but he's never been a pacifist. Not even in the Silver Age. He's never had a problem giving people their comeuppances. Look at all the crap he pulled on Lois during the 1960s. It was her comeuppance for all the crap she pulled on him, but today he'd be seen as abusive and misogynist.
I think the diner scene was simply a nice tag to wrap up that bit of business. Everyone in the theater cheered when he did it because it was a wish fulfillment moment where we vicariously got back at our own bullies, so it felt satisfying.