Salem

Bears aggro about everything thats in range of their roar/scream/that **** that instills fear in you.
Was running away from a bear, the bear leaving behind a trail of cricket, rabbit and timber rattler corpses, only to be stopped by a single deer who spammed his charge attack at the bear and saved my ass.
Is this intended or is it a bug?

Known issue that's been discussed since the creature AI changes. Nothing has been stated as to how it may be changed or fixed by the devs, but is currently "intended" as area attacks have no targets and will hit anything in range.

I think it's intended. Possibly not originally intentional, but it is not restricted to Bears.

Snakes will also attack other animals. I have seen snakes fight rabbits and crickets, and even other snakes. Once I even got two crickets to fight when I aggro'd both with a stomp, and then one used its secondary attack which has a small AoE and hit its neighbor.

So all of this leads me to believe that although animal-fights might not have been originally intended behavior, they are merely following the pre-existing combat framework without any exceptions.