ATC should not have given him priority, they should have asked him for his diversion field, and sent him on his way.
Ok, let's get this straight: ATC do not make operational decisions on your behalf. WE do not decide whether YOU should divert, we do not decide your fuel state (as it should be..how can we?) nor any other thing to do with your on-board situation. We just facilitate activity based on the info you give us The decision-making process will vary from company to company anyway. It appears, from this thread, that it will vary from pilot to pilot, even pilots from the same company!
If there is ambiguity about an emergency i.e. the information is unclear about exactly what on-board situation exists, surely we should take the safest action?