If you were PF, does your company SOP allow for you to enter instructions in FMC? It happens sometimes I know but if its his job as PNF to make FMC changes your quickness might have caused in part the confusion..You could have asked him to confirm the clearance, or asked again yourself? Either way you should both agree before executing and changes. Although with regards to some of the replies, I see no reason to make disrespectful comments about people based on such limited information about them or their reported actions. Having read your post again he doesn't sound like an Ego at all.