Fake field goal explanation

An interview with referee Ron Winters, from the Patriots:

The Patriots attempted a fake field goal with 7:18 left in the fourth quarter. Punter Chris Hanson complete a four yard pass to tight end Chris Baker for four yards. But Baker was called for illegal motion. Here is where it gets funny.

Q: What were the Ravens challenging on the fake field goal?

RW: The Ravens were challenging that the pass should have been called incomplete.

Q: Why did the illegal motion penalty not override that challenge?
RW: If it had been an incomplete pass, then they would have declined the penalty and they would have taken the ball at the previous spot. Baltimore would have – because it was fourth down [and an] incomplete pass – so they would have gotten the ball 1st-and-10 at the previous spot. So that’s why they challenged that, to determine whether or not it was in fact a completed pass. When we found out it was a completed pass, then the illegal motion penalty kicks in. [That] takes it back, so they have to repeat the down …. It was a fourth down. [He] caught the pass [and it was] good for a first down.

Q: So [Baltimore] challenged if [New England] had caught the ball?

RW: That’s right.

Q: Should the play have been spotted and measured before the challenge?

RW: There was no indisputable evidence to indicate that the ball was not a first down. We looked at that to see if it was in fact a first down. We couldn’t determine that from the replay. So the ruling on the field would stand in that regard.