Mihawk was originally introduced as someone chasing pirates to get their rewards. Guess Buggy placing bounties on the marines may have been one of his motivations why to hunt the marines for fun
Well one thing which makes this development interesting is the fact it goes in a total different route than theories which suggested he'd ally with Shanks. It gives him a different path, and judging by Buggy's "luck", this organisation might actually reach Laugh Tale, which could be Oda's way to make the Zoro vs Mihawk battle happening there