It could be, however i'm not really sure when it comes to the "s" thing because we usually stutter or prolong letters at the beginning of the words. But the rest could make me think he's a stutter because he repeats words and he has those kind of "ticks" (they're not actual ticks but they're movements we do while we stutter). Unfortunately none of us can answer the question you've made... You see, many stutterers get pissed when a person tells them their stutter is cute, but i personally don't really care. I don't know if you should tell him you noticed about his problem but you should definitely make him understand it doesn't bother you. I'm not an expert so i'm still not sure he's a stutter but in any case you should support him.