Wow. I believe it was Buddy's continuous throwing of the left hook, and then the left hook feint that set up the KO. Davis continued circling away from Buddy's left, which consequently made it easier for Buddy to land a right hand. Moreover, with all the left hooks coming from Buddy McGirt, Davis was not expecting a right hand. In the final moments, the throwing the left made Davis react, while preparing McGirt to throw a right hand with full power. Davis had no idea what was coming.

By the way, I fixed the video so that it can be viewed from this window.