With there barely being any free agents left that I want, Hump wouldn't be a bad move. He can rebound, and play tough defense. He didn't complain at all when he was barely playing to start his first season here.
Horford, Amir, Jerebko, Olynyk, Mickey
That's five big men, all of whom I'd prefer to give minutes than Hump.
Then you include the possibility of Bentil or Zizic getting a roster spot.
There's just no need for Hump here. My guess is that the team was looking at Hump back when it seemed possible they might let Amir and Jerebko go in order to create additional cap space.