Rex Ryan became a head coach in 2009. "spygate" was unleashed upon the Patriots in 2007, with the punishment coming in time for the 08 draft.
So, what Rex is saying is that he thinks Belichick is dumb enough to bribe an unknown quantity like a janitor, who could easily turn and talk to the NFL / media and set off a new, even bigger, cheating scandal that would have probably resulted in Belichick being banned from the game for a season or more, plus multiple picks lost, etc.
This is such a dumb concept to lend any thought to, but I think it's a pretty clear demonstration of why one guy is a now a talking ****face on BSPN and the other is coaching in his (rounding) millionth Superbowl this week.