As a thought, maybe - possibly - Quirrell anticipated the possibility of point 4 (Centaur.) It might be an effective way to make Harry look at his current goals (and their potential repercussions) from another perspective. I wouldn't think the anticipation would be that the encounter was certain, but if it were considered possible...

And if the homing version of "Stupify" is "Stuporfy," how ridiculously twisted would AK get? "Averder Kerderber?"