It seems the random encounter table that is responsible for deep ticks spawning always has at least one goblin archer too. You can't encounter a pack of deep ticks that does not spawn with a single goblin archer, and since they are placed in two opposing factions, they instantly start fighting among each other. The archer usually loses, but more importantly, I just found this odd and assumed it's probably not desired?

I think that was added intentionally to show the daily struggle in the Underdark. Goblin archers hunting deep ticks, or deep ticks fighting goblin archers, etc.

Alright then, it just seems so utterly random that I would have never figured it out. Should have been goblins fighting kobolds or something equally funny. (Of course I would never encourage making fun of midget fights..)