Problem with 'may' is that it creates inconsistencies and more decisions made based on the referee's interpretation rather than clear cut transgressions. Supporters are then up in arms because if it's a line ball penalty and their team gets away with it it's just a good shot, if the other team does it's a card-able offence. Personally, I prefer referees making interpretations on a case by case basis but it's always going to lead to outrage especially when World Rugby has been cracking down harshly on contact with the head.
Could Koroibete have been sanctioned, yes, did it affect the outcome of the game, no, is the player ok, yes, probably best to move on and hope for more clarity in the future.