What a handsome pup! I thought he looked a bit bull arab too.
My big boy was slightly stand-offish as a pup, but only a little, and he's turned out quite anxious in unfamiliar situations. I agree with what others have said about training and socialisation, but would like to add that the socialisation needs to be controlled, in a situation where he won't have a bad experience and maybe end up traumatised. Socialising willy-nilly with any dog or person without you knowing them has the potential to do more harm than good. Again, don't want to scare you, just keep it in mind when socialising him