Yes, the comic assumes people struggle with the order of operations. It does not however assume that of the reader. It is intended to make the reader assume that the character struggles with it and it's enthusiastically wrong rather than that they're using the ! operator.

At worst the comic is trying to be engagement bait and trick those people into commenting some variation of "Wrong, the correct answer is 24. You always do the division first," to which someone can reveal to them that they were bamboozled because "4!" is in fact 24.

Edit: and if they catch that it's like "Haha, you almost tricked me with that sneaky factorial. Well played." That's where the humor comes from. Whether or not it manages to trick you into thinking that they did it wrong.