Why? Is it illegal to land a helocopter where you want? A helocopter landed in my front yard when my neighbor had a heart attack last year. No one cared then?
It can be, depending on the airspace restrictions and specific FAA regulations governing authorized landing areas for aircraft. My suspicion is that the pilot knew better but took the chance, then tried to cover his butt by claiming a mechanical emergency.
I'm guessing that your friend was picked up by an air ambulance service. They have much more flexibility on where they can land, as a general rule, than the average commercial or privately owned helicopter, due to their unique mission.