can someone explain this clip to me

Bug, Ayaytrox R makes enemy Minions fear, but it's not supposed to work on ally Minions.

Minions were like "nah bro i'm out they ain't paying me this much"

"You got this buddy, the nexus is all yours."

That's the power of Baron my friend. Baron empowered minions gain a movespeed buff based on the average speed of nearby champions as well as slow resist. So Aatrox's ult feared them and they ended up faster while resisting the slow effects of the fear. Also since the fear lasts the same duration, they ended up traveling further than they normally would since they weren't slowed. It's like when you fear an ulted Yi and he runs away at mach 5.