Yeah I agree with you, I thought it was an odd pick too. I believe the Kings Org said something about him doing everything well when the drafted Hughes, but it seemed like there were better options out there. I just don't think we have a whole lot at the AHL level currently, so I don't really see why we don't give him a shot to prove himself. We've signed bigger longshots.
I'm probably the minority but I feel Greentree proved in the preseason that he was good enough to make the roster this year. I totally understand why the Kings sent him back to the OHL but he looks ready to make the jump to me. But I agree, it's not the Kings style to bring up a player so quickly and think he will be a strong addition to the Reign roster next year.
I don't track the European leagues but the below article recently came out. Maybe there is an option there (likely moreso than college currently).