Enforce or not???

[Mike51]

NF A1 drops back to pass. The ball is clearly thrown forward as a screen pass develops. A1 is under heavy rush, I as the WH, monitor any contact on him. No one hits him and I see the ball on the ground. OK, incomplete, I think, but here no whistle. Rookie HL gives the backwards pass signal, (you know points toward the backfield) A25 picks up the ball and runs for about 15-20 yards before being tackled. HL drops his flag.

Umpire tells me the pass is incomplete, as does the BJ.

I go to him and ask "wasn't that a forward pass"? "Yes, but it was in the backfield" he replies. "OK, so now it is incomplete", I tell him. His flag was for a five yard face mask on the tackle. I waved off the flag, put the ball back at the LOS and continued.

Should the penalty be enforced? would it make a difference if the facemask had been the 15 PF variety.

TIA