Davis said Kiffin is a liar, that he engages in propaganda to make the Raiders look bad, that Kiffin was responsible for many of the Raiders' bad personnel moves, and that Kiffin cannot be trusted. Other than that, it sounds like they have a great relationship.
An interesting side note came when Davis ripped ESPN reporter Chris Mortensen, accusing him of being a professional peddler of falsehoods. Davis clearly thinks Kiffin is the source of negative reporting that Mortensen has done on the Raiders.
Davis also said he would have fired Kiffin for his dishonesty no matter what the Raiders' record was, that he gave Kiffin all the authority a head coach needs, that Kiffin wanted to fire defensive coordinator Rob Ryan and that Kiffin never wanted to draft quarterback JaMarcus Russell.
Kiffin will have his say soon, I'm sure, but for now, Davis wants the world to think that Kiffin is a liar, and that's why he was fired.