So Ralm got volunteers to pretend to collect for Halpin and then turned in fraudulent signatures to knock him out of the running.
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.