It is the same thing.
Very likely happening on your client side only.
So what happens is that on the battlenet server the 3rd player which never played a game was already dead. So it was actually only you two remaining.
However, your client doesn’t get this information and for some reason shows that enemy as still active.
As a result it is shown as active, but doesn’t get any enemies - as this is done on server side, where he is dead already. Right after you died, your remaining opponent got the 2nd place - he never faced the remaining one… as he was actually not alive anymore.
Have seen many videos where you go 2nd and receive 300xp. Which should only happen for first place.
This happens as the first player was not in the game anymore, but your client doesn’t know that.