Strange decision by Oda to have Kaido face the attack head-on. Luffy planned to grab onto Kaido to prevent him from dodging the massive punch; however, this Luffy's plan was foiled because Kaido made him let go when he entered his Flaming Bagua state. Thus, Kaido could have chosen to dodge and subsequently kill Luffy with an attack, but he didn't.
The truth is, Kaido would have also overcome Gear 5; even though Luffy won the clash of finishers, he fell at the same time Kaido landed on the magma chamber. Both fell simultaneously, and only after the magma explosion was Luffy's victory declared. This could mean that, similar to the bombs, an external factor removed Kaido from the fight.