Amazingly, that is all there is to this joke. Instead of counting normally, he gets an overflow thing. But - that's it. He is making a mistake an old computer or simple program might make. But he is human! Does that strike anyone else as an ungodly pathetic joke? It's even worse than most other comics in the "blurring the line between man and machine" category.
I'm going to say this again, because the comic is so petty and simple that I can hardly believe it: The joke is that instead of counting like a human, he is counting like a computer. That is all.
Here's a theory I have: It is not possible to come up with a joke told entirely in numbers. Not counting if the numbers stand for letters or words or something, just with numbers as numbers, you will never get anything funny. Eh?