No, I've found this a lot ... it seems when you tame the only unit in the stack, it puts whatever the last critter was you killed over there under the defeated side. It doesn't seem to know what to do with itself when there's no units actually defeated.
Just noticed this is still happening in .87. Playing as Kulan, I killed a Butcherman. A couple of turns later he tamed a bear cub that was by itself, and the victory screen had "Butcherman" on the defeated side.
