I'm sure ATC understood the situation. Yet he wouldn't do anything until the magic code words were spoken.
Just because they're both native speakers does not guarantee that both fully understand a situation. Take, for example, the phrase "minimum fuel." Both pilots and ATC understand what this means, but saying it does not confer special priority on its own. The pilot may be running on fumes nd considering his or her life choices, but to the controller you're just one of 30 holding west of New York. Now, put a Mayday or Pan-Pan at the beginning and that means something vastly different to the controller.
That is why the below line in the FAA AIM is the last sentence in its paragraph.
Distress and urgency communications procedures are prescribed by the International Civil Aviation Organization (ICAO), however, and have decided advantages over the informal procedures described above.