Yes, it sounds like there was more to the story, and maybe Sweeney's hands were tied. In Hamilton's press conference in Calgary he was asked about him leaving Boston and he didn't want to comment about it. Another reporter then gave him the change to shoot down rumors that he wanted out, and he wouldn't comment.
I would have hoped that Sweeney would have shopped him around a bit more to see what else he could have gotten, but it looks like he may have been handcuffed a bit on this.