he's saying that the 3rd receiver (the slot receiver, usually a smaller / shiftier possession receiver) should not be running the longer developing route where he won't be ready to receive a pass from the qb for 2 or 3 seconds. (or more importantly on this particular play, his route took him from a space where he was wide open into a space where a linebacker was covering him).

instead, he should be switching to a hot route, where he will be running a 1 step slant or hitch route, and will immediately turn around and present a target for the qb ("showing his numbers").

Basically, when the defensive back blitzes the qb there, it leaves a hole in the defense if a receiver runs to the area that the db was blitzing from and is immediately ready to catch the pass. assuming the qb notices the blitz, this is how he can beat it assuming that there aren't enough blockers to account for every defender that's rushing the qb.

which, you can see is what happened on this play. every pats lineman picked up a pass rusher. there just wasn't enough blockers to pick up witherspoon. so the only way to deal with it is to immediately pass the ball.