They didn't "fight" exactly.
Chris was bouncing in a night club when Tyson slaped him behind the neck, then he (Tyson) stood in "fight position" and was yelling "c'mon muthafucka" and stuff like that. Cormier did nothing about it.
Yeah, that's the story. Apparently Mike was joking around. I don't blame Chris for not wanting to get into it with Tyson, obviously. But if it
did come to full engagement, and Cormier didn't lose his head with the reputation that comes with Mike, I believe he could have at least neutralized much of what Tyson could dish. Again, as long as he could avoid direct-to-the-head shots. Chris is a strong dude. Coupled with aggression and an ability to remain relatively calm, the fight wouldn't have been a given.