He begins to say 'no', of course not, a little over-excited, perhaps, an altogether unbecoming quality for one such as himself, but nothing that would earn such a nickname. But he sees the chance to explain away the title without any mention of magic and his association to it, so he stops himself.

"Yes, I must admit, I rather was a nuisance. But, well, we all clean up our act in time. Yet nicknames are never forgotten by old friends. Nor oneself, it would seem." Ignoring that he hardly looks twenty, some people age well, of course! There is nothing strange here, don't think about it.