Confused about the keyhash that in facebook android sdk

I m working with facebook sdk for android, and I ve red almost every documentation I ve found about it, but what confuses me, is the keyHash, I ve heard that its made for security, and in this slidenerd tutorial Mr Vivek says that its supposed to be secret, but he didn't remove the code which generated it, and anybody who can have that same code could generate the same hash since there its not a salted hash. I m a bit confused about it, so please tell me what I m missing. thanks in advance.