Seth came up short on that kick and Kimbo thought he would rush in and try a lil' take down - take down. That is why he came in low, not because he slipped.
Seth threw a punch that caught him and pretty much put him out.
If you look at all the other punches that Seth threw while Kimbo was down, on his side and then back, Seth probably threw about 8, but only about 4 really connected. And the strongest of those was that overhead hammerfist that he whacked him with. First two punches ended the fight, the last ones were missing and really nothing more but icing on the cake to make the ref stop it.