“Misprize common sense at your peril is my motto.”— Kingsley Amis, Stanley and the Women.
It does say that the piece of hamburger was about half of the hamburger, friends tried to do Heimlich but "were unsuccessful due to his large size", there were nurses at the school for a blood drive who worked on him & could get part, but not all of the food out, and they worked on him for 45 minutes at the hospital before pronouncing him dead.
This article has some additional information - it says the student was walking & tried twice to cough the food into two different wastebaskets in different areas of the school bofore collapsing and being taken to the school clinic in a wheelchair. It also says the Heimlich maneuver was attempted, but that the student weighed over 250 pounds and they think that's why it didn't work properly.
A third article has similar information but none of these three mention that help was delayed or denied because students weren't allowed to use cell phones.