Kelly has a couple of things in his favour. Right now his agent can point out he is in the Scotland squad for the Euros and that is worth ~€50K in payments to his new club just for being there.
The link with Celtic kind of makes sense if they are worried about European limits on homegrown players. What are the other options for a Scottish goalie? He isn't really any worse than Bain. So if Celtic want to continue to focus on bringing in guys to sell on wasting a valuable international spot on their European roster for a sub goalie doesn't seem like a smart idea.