Steve is with him up until Tony speaks about how deeply him not showing up to rescue him bothered him. His confusion only grows when he calls him an important person. He doesn't consider himself anything to Tony other than a teammate; someone he could have had history with, but didn't. He doesn't expect Tony to feel even that much. His behavior seemed to confirm his suspicions. He was just an action figure to pick up and set down at his leisure. Now that he cooled down he concedes that Tony may see him as a valuable team member worth protecting. This though....
"What?" He's got nothing. He can't wrap his mind around it. "Oh. Because I'm Captain America, right?" His gaze flicks to the side. He feels stupid suddenly. Of course he isn't personally valuable to Tony. His status might be worth something. It was to Howard evidently after he "died."