Yeah, okay. Just looked it up. Live and dead ball are considered part of the same play according to one of those Mike Pereira things. A 15 yard penalty supercedes a 5 yard but that wasn't the case here.
Caught a 50 yard bomb starting from the Eagles' 2 yard line so it was a huge play. He tossed the ball at the Giants' D coordinator and did some light taunting on their sidelines. Got called for taunting + Giants' penalty meant that it got called back.
Pretty crazy how that works. Essentially the Giants committing a penalty helped them and hurt the Eagles because if the hadn't, they would have just subtracted 15 yards from the end of the play and it still would have been a 35-yard gain.
Makes you wonder, what happens if a receiver gets flagged with a dead ball penalty after a touchdown reception (meaning the penalty yards are added to the kickoff instead of negating the TD)? If a team on the defense notices a flag for unsportsmanlike conduct, taunting, etc., they could just commit their own penalty by, say, pushing another player to the ground or whatever. Penalties offset, TD is negated.
I hope the NFL takes a look at this rule. Either enforce both penalties (in last night's game, this would result in a 50 yard reception + 5 yards - 15 yards = 40 yards net) or always enforce dead ball fouls after the end of the play and don't allow them to offset (unless perhaps both teams commit a dead ball foul).