This is my guess as to how this all went down. After Devers spoke out about not wanting to play 1B, and basically calling out Breslow and others, Breslow went to Henry and said he wanted to trade Devers. Henry said "hold on here" and went to talk to him in KC, figuring he could smooth things over. Devers probably didn't change his tune one bit so Henry said "OK".
As to the trade itself, it is always going to be hard to win a trade when you are trading the disgruntled star, and Devers is a hitting star. He is also injured a lot and may never play anything but DH the rest of his career. There are recent precedents; Nomar, won a title; Mookie, played at an MVP level for multiple seasons, Bogaerts, he is hitting 0.231 with 3 Hr this season (worse than Story). I don't think this trade will turn out as bad as many seem to think right now. We probably won't win the World Series this season and this probably won't be as bad as the Mookie trade.