Enchanter Faction Question

[Mzy12345]

On a high elf enchanter I was able to kill Troll guards until "faction cannot get any worse" and with illusion troll and faction buff I would con dubious.

I was with my brother there the other day who is a dark elf enchanter and after killing them for awhile he is now kill on sight even with illusion and faction buff. Both are agnostic for religion. Anyone know why this is the case?