It all makes sense to me.
The Sabres only have two options with the CBA and all the league agreements - keep him at the NHL level or release him back to the OHL.
The OHL must have an agreement with the KHL, based on Zadorov's agent, where the KHL needs to approve a player to play in the OHL. In the case of Zadorov; they do not currently have that approval which would mean that he would have to go play in the KHL.