Spurs are well within their rights not to sell him. It's a dick move if there was some kind of good faith agreement but technically a contract's a contract.
The problem for us is that we have no clue what that agreement was, and what's been reneged.
Maybe Levy has changed his mind and said he won't sell him (although there's enough evidence to say that's not the case)
Maybe he's changed his mind and demanded too great a fee (too great from City/Kane's perspective)
Maybe he's changed his mind and told Kane to wait longer than he would have liked.
Maybe he's not gone back on his word, and Kane is the one misbehaving here.
Maybe they've both simultaneously screwed each other.
Maybe there's less in this than we think. Maybe there's more.
We don't know. I understand it's a pretty boring and obvious statement, but we're all so in the dark it's just too difficult to know who is or isn't in the wrong here.
Does it matter? You are right, we don't know. Many had gentleman's agreements with their bosses they'd get pay rises. Then covid happened. Some may kick up a fuss, some may be happy to have kept their jobs. Depends on the circumstances, and the person.
I don't think it is that much of a crucial arguement in this. Kane wants a move, the club he wants to move to is willing to offer Spurs a significant fee. Gentleman's agreement or not, he is drawn into pushing for it because he wants it. Gives him more of a public display, whether or not it is true, and he will use that.