My understanding is he held onto the rim in a dunk, and then slipped off it and landed awkwardly.
I recall many years a go when a young kid named Darryl Dawkins fresh out of high school used to destroy backboards on dunking--in a kind of macho expression of immaturity. The League fined him, and made dunking illegal. Or at least some aspect of it, as I recall.
Later on, Stern succumbed to the entertainment demands of TV and permitted dunking. This was about the time the rival ABA was competing with multi-colored balls and 3P shots. Backboards were strengthened. It's almost impossible now to tear a rim off a backboard, no matter how long a 250 lb player holds onto it.
Nowadays, dunking is routine. There is even a contest at the all star game on who can twist the most in the air while dunking. Mainly TV showtime stuff. And the kids coming out of school like Brown and the like soar through the air and grab the rim to break their fall. It can be dangerous. I remember Dee Brown wrecked his career, blowing his knee out on one of those monster dunks.
Maybe it's time the NBA ended the practice of hanging onto the rim after dunking. Will it make dunking safer? It might--if only it prevents kids from trying to jump out of the building.