He got it before the Duchene trade.
Chiarelli was another finalist. I don't pay close attention to the NHL awards, so I assumed that it's the type of thing where because it's voted during the conference final, it skews to the GM of an overachieving team, but looking at the last few winners it seems pretty fair (Jim Nill has won a few times).
Dorion did make some big moves (Brassard, Burrows) - but I don't know how significant of a role they actually played in the run. Brassard had his moments, but he didn't quite come as advertised. I am probably in the minority that I think the Phaneuf trade a year earlier was brilliant if you consider how dire the Senators situation was with their need for a top 4 defenseman and their inability to shed cash/spend. But if I recall that move was more Bryan Murray, although I could be wrong.