As was his right. He felt that the offer was so derisory that he didn't want to engage. Having seen us pay £100m for Grealish, it may have altered his perception of what is/isn't good value. Nobody actually knows for sure what City offered.
There is no yardstick for what is a fair offer. A player's valuation is subjective in that it is what he is worth to both clubs. Levy had the player under contract and expected him to honour it, barring an offer of epic proportions. It is not unreasonable behaviour to keep a player that means a lot to you, is under contract, and would be virtually impossible to replace.
People here would have no problem if Txiki didn't pick up the phone to Levy if Spurs wanted Haaland or Rodri for £150m. I know I wouldn't. By your argument, Txiki is being unreasonable.