There is one thing that Tony wants remembered about this moment if anyone thinks about it later, in any future retellings, and that thing is that he definitely does not make any sort of noise at being caught out in his staring. Nothing potentially embarrassing, or startled, or anything like that. He does jerk though, his eyes for just a moment torn away from the sight in front of him to the person who has come up beside him.
It doesn't take a long look for him to feel fairly certain that this is the other version of himself, he didn't look long, less because he was more interested in the sight of Steve in the water, and more because the longer he looked the more aware of the differences between them, and more than that the similarities. So yeah Steve was a much safer place for his eyes.
"How can he not realize?" Because he had to right? He had to know what he was doing standing there like that all wet and helpful and full of .... patriotic righteousness.
But he thought of the Steve they'd left behind and well - he could probably say the same thing for him, when he worked out in the park, when he was dancing at Club A, Steve had never been the sort to think about what he might look like to anyone who saw him doing those things. so why should this one be any different?