You are about right
I retried, and a patrol does spawn as long as you progressively go through the fight. In other words, if you kill the boss instantly it does not trigger - it does only if you slowly bring him down in health.
That being said, the patrol on Zero is made of 1 single Ogre, while on Retail it was composed of
- 1 Bloodaxe Veteran
- 1 Spirestone warlord
Also, apparently the patrol comes up at about 70% boss health level, when boss emotes "calling for help".
see here
PS - I'm of course talking about the patrol that spawns after the boss is engaged. There is another single-mob wallking patrol before the boss, but you need to kill that before engaging the boss.
Ciao
U