You know what's funny about the COY thing (aside from the Raps twitter account tweeting about "congrats coach" when Casey was listed as a finalist for COY) is that the award is based purely on the regular season; is Stevens' regular season case that much better than Casey's? Toronto won 4 more games than Boston, Boston had Irving for most of the year, Horford is an all star, two top 3 picks, etc.
I'm not saying it's hands down Casey (but I bet he wins, which will be funny) but more that the playoffs is making it look like Stevens is the obvious choice (and to be clear I think Stevens is probably the best coach in the league, him or Pop probably) when based on the regular season (which is when the voting is done) it's somewhat close.