Kinda of a bad video, but that is really him dunking. I believe this from the documentary that came out recently.
That is indeed from the documentary. I recommend watching it if you have not. It really helped to show how special Julius Erving is.
I hope this link works... (Watch it before it gets taken down)
He dunks right around the last minute of the film
Uncle Drew strikes again!!!
Impressive! I am half his age and this would be me if I tried to dunk now.