From my understanding he said he'd buy twitter, they started a whole process of running numbers and preparing everything, told him how much it'd be, he said yeah, they kept preparing all the legal and financial stuff, which cost a lot of time and money...and then he said "nah it was a joke"

That's not what happened and that doesn't even make sense. Obviously, he knew how much it was going to be. He had formally submitted a buyout offer (so he definitely knew how much it was going to cost) and then later on, he started backtracking.