I have hundreds of pictures over the yrs of deer standing on there hind legs and smacking another deer on the nose, fighting for there turn at a feeder/pile of food/mineral lick
even my sig pic, shows one fighting LOL

that would explain things to me
they hit HARD too, many times been in a tree and watched them fight, the sound of the smacks, is LOUD< wouldn't be suprised if its nose was maybe broken, and thus the swelling!
nothing you can do about it, its pecking order that drives them toi fight I think1 LOL