I say 360 but you are right it is still very cool. He starts off with his back facing the basket and he dunks it with his back facing the basket.
You have got to be nuts if you think that dunk was a 360. He starts with his back to the basket and finishes facing the basket, = 540 degrees. Check out the slo-mo for proof.
I think he faced the other side of the court (back to the basket) when he started the jump and faced the bottom side of the court on the screen when he dunked the ball. So it was 1 1/4 full spin or 450 degrees.
I thought during the slow motion and pause it looked like he dunked it over his head with his back facing the sidelines while he was in front of the basket........It's no big deal. not the dunk but whatever degree it is.