Cripes, here we go again. Yes, Mayday is "Save our souls" ; Pan Pan Pan is a state of urgency. One out of three hydraulics failing is not, in itself, a state of "Emergency". Sounds like there were other failures going on that led the guys to elect for an immediate return , declaring a mayday, preparing for overweight landing & limited braking. A single hydraulic failure, out of three, in itself would have me run the check-list and then ask the Senior Cabin attendant what's for Dinner .