Yeah it was a kind of release against everyone - media criticism, appalling officials, probably what he saw as a lack of support from Giuntoli (which, for me, is fair, considering our mercato and the imminent sacking that we all knew about) - and in his mind he was probably thinking, "fuck you all, I still won the Coppa and got a CL spot", which he probably sees as a great achievement considering. I don't particularly agree with that notion but I can definitely see where he was coming from.
Does look like yet another classless move from the club, but I don't think it'll have a huge impact at this stage of the season. We also don't know what he said or did to Giuntoli and others, it might have been a complete meltdown and burning of bridges.