They didn't have to say MAYDAY, EMERGENCY or PAN PAN. The controller knew immediately from the radio transmissions and what the crew said, and their responses to his inquiries, and by watching the a/c descending, that this was an absolute emergency.
He responded immediately by notifying LGA tower to stop all departures, thereby reducing his workoad and clearing the runways of aluminum.
After flying into NY for years you recognize the voice immediately.