The “patrolling” he is talking about could have a big difference in the infernals behavior and could be why it’s not working correctly.
Edit : www.youtube.com/watch?v=zWGKVPQ2LZ8
Look at 1 minute 48 seconds, the infernals immolate aura DOES NOT hit the low level standing under it, with his PvP off. The low level also did not attack it.
The video is from 2006, so no the GM is not gaslighting you