Punters and kickers at all times fall within the definition of defenseless players. This means that they can’t be struck by an opponent with a helmet or in the head or neck area.
In this specific case, Garvin hit Huber with a helmet in the head, breaking Huber’s jaw. A flag should have been thrown.
Don’t be shocked if the league admits the mistake during the week. Even if an express admission isn’t made, the fine that inevitably will be imposed on Garvin will do all the talking.