I think he's pretty pissed with Wilder and the WBC. Whyte sat at No 1 with them for a couple of years and couldn't get within a bull's roar of Wilder, then the WBC took his ranking before he was found guilty of doping. The WBC have since reinstated him but he still seems at least a year away from a shot at the champ.
It looks more like a rivalry between Hayman's Professional Boxing Champions and Hearn's Matchroom. PBC only have Wilder's WBC belt, while Matchroom has Joshua's IBF, WBA, WBO & IBO titles. With Joshua now having to choose between dropping his WBO or IBF belts and choosing to defend his IBF against Pulev, it looks as though the then vacant WBO title will probably be fought between two Matchroon fighters Usyk and probably Parker. If so, and Joshua beats Pulev, then Matchroom will still have all the belts except for the one held by Wilder. And I don't think Hayman or the WBC want to risk losing that belt against a Matchroom fighter in the shape of Whyte.
It looks like Dillian Whyte has been a long time victim of boxing politics. I think he's just had enough and is willing to try anything to draw out Wilder.