Red beast spawned in wall did not summon support mobs

Map: Ashen Woods T4

The red beast was a small monkey species type, the one that you encounter in Act 2 Riverways.
It spawned inside one of the walls (the kind of which you see in the picture below).
I was using Double Strike with Ancestral Call linked and wasn't in melee range for it to hit me.
It did not spawn any mobs as i was hitting it.
If it matters at all, I killed a yellow beast nearby, right before it.

https://imgur.com/gallery/0w2QKWq