It's a good point regardless, though, and I don't envy the position of trying to draw the line between what's protected speech and what's not.
Edit: it seems the cake was not requesting custom writing -- custom writing was explicitly protected as free speech in another case. It seems in the analogy of the burger joint, that case was more akin to a burger joint which only sold "I endorse your decisions" buns. Which makes me as glad as ever that I'm not in charge of being the arbiter of what's speech and what's not.
I’m fairly certain it was, it was a wedding cake after all. However people love to drop details and make it worse.
There were other lawsuits, such as a case in Ireland that involved writing though
Do you have a citation for that? I've also seen reporting that there wasn't an actual couple, and to be honest: I'm having trouble figuring out what's real here.