May I ask : Is your chest possibly large or could you see a good definition of it ?
I feel he looked at your chest because he was curious and he liked what he saw. He looked at it again and then looked at you.
He might be a breast man. He might be attracted to you. He might stare at your chest instead of arms / is kinda hard to believe/ because men are mostly fascinated with the mammaries
But the biggest thing here : How did it make you feel ? Uncomfortable ? Nervous ? If you like him, did it make you feel excited that he was looking ?
Either way. He should not be looking. He saw and now he knows what your chest looks like. If he stares at your chest again , then you will know he simply likes your chest.
If you feel offended by any of what he is doing , you can report it.