Is there any guideline the NFL uses to refrain from calling a penalty due to unusual celebrations or mass reactions?

Question

In the NFL's NFC Divisional playoff game on 2018-01-14 between Minnesota and New Orleans, Minnesota's Stephon Diggs scored a touchdown as time expired in the fourth quarter to take the lead and thus win the game. Of course, the game does not end till the PAT is attempted.

Diggs removed and threw his helmet in jubilation. The back judge threw a flag, presumably for unsportsmanlike conduct, but this penalty was never announced. Why not?

The players, media, coaches, staff, and security rushed the field. After about ten minutes, the officials were able to get everyone off the field and the Minnesota offense on the field for a PAT attempt. Why was delay-of-game not called against the Vikings?

The Saints were not there, and it took another minute or so to get eight Saints onto the field and onsides before the Vikings could snap and kneel-down. Why was delay-of-game not called against the Saints?

The real reason is, of course, everyone had been caught up in the moment; it was an exceptional ending to the game. Further, any penalty would have been toothless and silly.

Is there any guideline the NFL uses to withhold a penalty call due to unusual celebrations or mass reactions like this? Or, did the officials simply use their discretion to avoid a silly but correct call when it doesn't matter?

Answer 1

Peter King got an answer specifically to the part about Stefon Diggs's helmet:

DIGGS HELMET THROW
Why wasn't a penalty called on Stefon Diggs when he threw his helmet immediately after scoring the touchdown at the end of the Vikings-Saints game? As you may recall, this happened against my Cleveland Browns when Dwayne Rudd threw his helmet back in 2002 during a game with the Kansas City Chiefs. Why would this be treated differently? It cost us the game.​ —Michael G.

I asked a league official in the officiating department this question, and the answer came back that a foul like this would be enforced on the ensuing kickoff. Seeing that there was no ensuing kickoff because this happened on the last play of the game, there was no infraction.

However, one might wonder if this was really the decision process followed by the officiating crew at the time.

ALSO: see this PFT Commenter humor piece suggesting Peyton Manning should have been suspended for excessive celebration after play stopped for several minutes to celebrate Manning breaking Brett Favre's record for career touchdown passes.