Actually, if you watch closely enough, the jar starts out about half full. In the next shot it's about 3/4 full, and then in the next, it's about half full again.
The mixer was never full, it only looks full when it's switched on, as you would expect it to. It's actually only just over half full. He starts drinking, the camera goes off him, and when it comes back, assuming he's been drinking the juice, it's now just under half full. Nothing superhuman about that!
This may sound redundant, but when a blender is in use, the contents fill the entire blender. When it is turned off, there is still juice on the sides, but the majority is at about the halfway line. He never chugs the juice. For the record, he made carrot juice, not orange.