Why would a guy get dumbstruck when you talk to him?

So when I came to class, a water bottle was lying on the chair I usually sit in. This guy, who I've caught staring at me twice or thrice (from the corner of my eye) and who has even butted in a few times while I'm having a conversation with someone else for e. g. I'll ask someone a question and he'll answer it, he'll give his opinion even though I don't ask for it etc.

He was sitting behind my seat so I asked him that does this water bottle belong to you? And handed it over to him. He looked dumbstruck and like he was in a trance or something lol he just nodded his head from side to side (meaning no I guess lol) and still took the bottle lol. After some time, I asked our teacher a question and he answered it for me 😅
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By the way, this was the first time I've actually talked to him.
Why would a guy get dumbstruck when you talk to him?
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