DN wanted to keep Diego, yet Marotta had other plans. That is what concerns me the most, especially since part of the reasoning for signing them both was because they worked together effectively at Samp. Now Marotta is going over DN's head and selling players he wants in the team.
Ultimately, I think it had more to do with getting rid of Diego's wages, and DN wasn't too bothered because he got more of a goal scorer in return, which is more ideal for his beloved 442. Hopefully it was a one time thing, but you can't help but think if this is going to be a repeat of a situation we have already been through twice with DD and Ranieri, where the coach and management disagree on who stays and goes.