I agree with Eric. To add a bit more . . . "A something or TWO," is a common expression. It can be applied to almost anything. So, the joke is that he says FOUR instead of TWO, meaning there are a lot of malls.

Hey Alam! Great question. Here the speaker/writer is making a joke, saying that there are many malls in US cities. It's basically saying, "Let's be honest, there is usually more than one mall in an American city."