Probably a situation he inherited though.
Dunn was polite about it, but he had already made up his mind to get out of here. Looks like Dunn is tired of playing on a losing team and wants to go to a contender, based on what has been said about him liking LA and Chicago.
IMO, given the situation Walt inherited, it was the right move to trade him. I'd rather have the 3 players we got for Dunn than the 2 draft picks as well (assuming the Reds did offer him arb, knowing he'd decline).