I've had 2 oscars at separate times, one was very social and would always greet me whenever I would come up to the tank. The other one was the opposite and seems to be like yours, very reserved and docile.
Hey oscars are great i used to have one that would jump up and take "treats' from my hand, he really like to be petted too. but now i have one that is really unsocial and he just wants food wont do anything cool for it.lol anyway i think it justthat i havent had the time to give him the attention he needs. but anyway i had this long finned rosey barb in with my one oscar since he was little he never botheredhim even when he got huge and the little bard was still only like 2 or 3 inches.