Nobody was paying attention. That is why Codey was popular.
Codey's popularity might have something to do with his in-person
threat (while visiting a radio station to tape his monthly show) to beat up a radio talk show host who made some ugly remarks about his wife's bout with postpartum depression, and then refusing to apologize to the talk show host for standing up for his wife. That's probably the most memorable thing he did during his brief tenure as governor (other than not getting involved in scandal and not hiking taxes, like most other Democrat Jersey governors).
As for this poll, I'm skeptical that Menendez will lose. He just started running TV ads in the New York City market, trumpeting his role in defeating the ports deal (and standing up to President Bush), and his role as a prosecutor attacking corruption. I have yet to see a Kean ad on broadcast TV. I expect Menendez' poll numbers to go up. I don't think he's going to pull a last-minute switcheroo, either.