Harry was so stunned by Colin's appearance that he didn't even have time to react to the hug. Actually, his first reaction was to worry that he'd get Colin sick. In retrospect, that probably meant that he was feverish, and that the fever had muddled his mind; probably not a good state for him to be out and about where someone could find him this easily, at all. But it hadn't been a dangerous person that had found him, it was Colin.
Excitable Colin, holding the same camera that Harry recognized from school, still taking pictures. "You-- what are you doing here, Colin?" he asked, unable to react fast enough to hug him, except to awkwardly put a hand on Colin's shoulder. "Are you on the run?"
He ignored the questions about his health. Not that he really thought the information would hurt Colin, but he didn't want to make him worry about him. Harry was supposed to be fixing the world, after all.