Why did he tell me this?

Me and my best friend (a guy) were just talking about gyming and how he needs to join it again.
So since he has left the gym and rejoined it many a times I just told him to not leave it again and he was like "haha chill I won't leave till I get a flat stomach"
But why did he specifically asked me to "chill" like I'm not his girlfriend or anything that I would want him to get a good body.. I just advice him.

And we are really close and we also made out once but are not friends with benefits coz we have clearly spoken about it.

So did he think that i want him to get a good body or was he trying to say something else too and I've told him that he's getting fatter day by day.
Does he want a relationship with me by any chance? Or is this how girlfriend and boyfriend talk? Stupid question but yeah I have no idea about all these relationships and stuff coz never been in a serious one :3
Why did he tell me this?
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