Too complicated. If Halpin was paying folks to get signatures (I don't know if he was), then I can see folks padding the petitions for a few extra bucks.
Or they could just be exta-enthusiastic, in a Chigago sort of way, and maybe Halpin didn't pay enough for the signature checkers to look the other way; or Rahm's team out-bid them.
Even easier.
“Everybody” always collects fraudulent signatures every time. (That’s the “Chicago way” you just have to collect more fraudulent signatures from approved frauds for approved frauds to get in the chosen elections.
It’s just this time that Rahm (obviously!) CHOOSE to combat the fraud and get a (staged) hearing where they were revealed as fraudulent.