It's more than just 'going to the zoo' to learn. I spent months there and didn't really pick up on the way they turned their entire upper torso
until the very end of my stay. Sure, if the film is a hoax the hoaxers could have done the same thing but this is just one piece of additional
realism that adds to the overall believability of the film.
I don't know if the film is the hoax nor do I know if it is 'the real deal'. Some experts have pointed out realistic muscle movements, supposedly
showing that the creature is indeed a real creature. If that's the case, we have the possibilities of a real creature rather than someone in a
suit.
If it's a hoax, it's one of the best ones ever made. The person(s) behind it had excellent knowledge of big apes, and quite possibly one of the
most advanced 'gorilla' suits ever made (if indeed it is a suit, it blows away the cheesy planet of the apes costumes).