I don't think that is the correct interpretation. It's not that it's through paper that it's "Little Bobby Tables". Little Bobby Tables is an injection through someone's name.

In this case, the reference is because it's through the voter registration list--i.e. voters purposefully put a SQL injection in their voter registration.

The analogy breaks down if you look too closely because it's in the party name field, not the voter name field. However, I think it's funny enough to stand notwithstanding the fact we're sitting around analyzing the joke.