I thought it was a good challenge. That wasn't interference IMO. There is no face guarding in the NFL.. the WR initiated the contact with the DB and the ball hit the DB in the back, not even sure it was a catch-able ball, it was 3 yards short with the WR running the other way.
But either way, you don't hold that flag in case you lose and need it later. There are times you take your shot, if for no other reason to show your player you go their back. And I am not sure that the play you are referring to could even be challenged. I don't remember where the ball was when he was being molested, holding, illegal contact are not review-able and if the ball wasn't in the air, then it's not pass interference.