Seems like a good move for him! He's good enough to get a serious shot at being the starting keeper at a high level. Hope he ends up doing well and they don't get relegated!
Contracts exist partly so you can sell the player during its tenure. Having a player sign a contract only to run it out and leaving for free is not a strategy for long-term financial success in football asset management. Plus, with Raya and Ramsdale, Turner was clearly weakest.