So I guess the only way something like this would happen is if Horford demanded that he gets signed and traded for Boston's package of assets in order to 'hook up' his old team. Obviously that doesn't make sense since he would likely want his new team to be as good as possible, but there can't be any other explanation for it...unless this occurs after Boston signs other free agents and gets near (but not to) the cap.
Anyway, no reason to justify this - I completely agree, worst idea ever.