T'wasnt fake. Will Smith was triggered by a perceived attacked on his wife who is privately mortified and scared over illness which resulted in hair loss. Because Will Smith had to watch his father physically abuse his Moma as he watched defenseless. AND he was still in character with Richard Williams, father of Venus and Serena (for which he won oscar) who was ALWAYS up front protecting his daughters while arguably abusing them with tennis coaching.
It also didn't help that Will's wife had a short affair which became public and which Will Smith denied. But two presenters joked about her, one who earlier suggested Will Smith was on the market and wrong time wrong place Chris Rock joked about her playing "G.I. Jane 2.0" with her new hairstyle.
So confluence of everything led to Will Smith lashing out and actually slapping Rock. If it was fake, Rock would've had a much better comeback line than the one he barely got out while still in shock over what happened.
Oh yeah, that awkward profanity laced exchange afterwards…
Don't shoot the messenger but this entirely plausible explanation is what they are running with.
Probably the underlying overall PANIC in Pedowood was a factor as well.