It wasn't long before the smoking crator and sirens had drawn Cap from the tower, telling JARVIS to notify the others. He'd been off training during 'Iron Man's' attack on the twins, and he wasn't about to be caught staring off into space this time. Tony needed him, the twins needed him, this suit needed to be stopped.
When he reached the scene of the destruction he was stayed in his steps a moment, taken aback by the mass of it all. All those people. Gone in an instant. And the suit looking down on it all in a calm manner.