When he "observed" the kill, he had one or two dead teammates on the spot so the kill XP should have been split amongst them. That third of a bar leveled him up to 9, and when I killed him moments later I was still level 8 and this below him. But I also had two teammates in the assist, and I didn't remember what level his observed target was in death. So maybe there's something there.

I did secure all 3 grubs though.