Kimbo is strictly a stand-up fighter. His people knew Gannon was an MMA guy and 'tried' to make rules to prevent Gannon from making this an MMA fight.
Unfortunately, Kimbo's representatives were ignorant of MMA and Gannon was a little shady in letting them craft their half-assed rules.
The rules Kimbo's people wanted were 'no kicking and no ground fighting'. Gannon had them clarify what 'kicking' meant and they said feet and shins. He giggled and filed in the back of his head that they forgot to include knees. Gannon then had them clarify what 'ground fighting' meant and they said no takedowns, ground and pound, or submissions while on the ground.
Once again, Gannon giggled and filed in the back of his head that they said nothing about standing submissions like the guillotine choke.
Net, Gannon fought within the agreed upon rules, but he did so by taking advantage of the idiocy of Kimbo's representatives. He knew full well that Kimbo's people wanted a pure fistfight with no grappling, but he capitalized on their lack of MMA knowledge to leave some loopholes for himself.
I'm no Kimbo fan, but I will give the guy some credit. He's got some serious raw skills. He has fast hands, KO power, decent boxing technique (by MMA standards), and is a good athlete. If he spent a few years training in grappling, he would actually be a dangerous MMA fighter.
Unfortunately, the people who 'represent' him are making way too much money by having the poor sap fight in backyards and basements, and Kimbo ain't bright enough to see that they are taking advantage of him.