We never confirmed that he was actually in our realm -- in fact, from what I've gathered it seems he never was. I don't see anything about it on his family history, he wasn't on the character list, and he didn't receive any realm wide messages. Oh, and he was in a battle with our realm's forces at the mountain after the takeover but before the allegiance change.
That would be part of the bug. Cleanup scripts would have silently 'corrected' his allegiance to your realm when they ran (haven't yet checked whether they did or not, but my guess is yes).
