Game Mechanics: Skeletons in FoB communal with Scorpions

[Vega]

I'm pretty sure I'm not just messing up aggro, and have seen this a couple times. If I pull a heartsting scorpion, and it paths near or over a greater skeleton or lesser icebone, the skeleton will add. I looked around and couldn't find any evidence that these should be communal on Alla. Perhaps I'm looking in the wrong spot, but it does seem like an odd combination to assist each other.