Dean Blandino explained that the actual blowing of the whistle doesn't need to occur for the penalty to be called.
Yes, the referees are at fault for not blowing it. Sherman is also at fault for roughing the kicker after the ball is declared dead.
http://profootballtalk.nbcsports.com/2016/11/08/walt-anderson-explains-dean-blandino-says-walt-anderson-is-wrong/
Also, the relevant language in Rule 12, Article 2, Section 6 of the NFL Rulebook explains the following as Unnecessary Roughness:
"(g) unnecessarily running, diving into, cutting, or throwing the body against or on a player who (1) is out of the play or (2)
should not have reasonably anticipated such contact by an opponent, before or after the ball is dead "
Flag down, officials running in, Carpenter has a reasonable expectation that he shouldn't be hit.
No question it's a penalty for Unnecessary Roughness.