Yuya at least doesn't notice his fitness level enough to point it out. He didn't really expect Strange to be secretly beef under his coats. Besides, if he stats doubting Strange's ability to swim it'll fall into a cyclical crash and fail.

Rather, what he does notice is how far those mirror scratches on his arms go once the robe is removed. He stares for a bit too long before bringing his attention back up. "You're taller than me, so I can show you how to do it before we get deep enough that you have to swim."

He takes off his pendulum, the only accessory he's kept on, and sets it on the towel by the bank before he wades into the water, just expecting Strange to follow.