Taking a broader view of the situation, a baker in Colorado went all the way to the Supreme Court for the right to decide who he would serve and who he wouldn’t. If he has that right then so does this restaurant owner.
I don't think the court ever entirely decided that. Just that he was treated unfairly by the civil rights commission. There is still wiggle room for future cases.
Personally, I think the owner should have had a sign on the door that read Trump voters and officials are not welcome. There are plenty of other places to buy $30 pork chops.