No, that guy really shot him. Everything after he lost consciousness, that was the halluciation in his head.
That's not what he was asking. He was wondering if the reasoning for the shooting was the real reason or was that just in House's head. More than likely House recognized the guy on some level and inside his mind he put two and two together or it was some sort of guilt for telling her that the guy had an affair, which manifested itself in House's dream as the reason he shot him. Hope that made sense.