Khudobin's contributions are: 21 more points than last season. Almost 500 less minutes on ice for Tuukka at the end of the season (assuming he starts the Florida-team games). One stretch of 5 straight when Tuukka was struggling that was the start of the hot streak that this team has basically been on since about game 10 of the season. He's a backup, but his role as a backup has been far exceeding what is expected of a backup. ....and that's what this award is for. The person who most exceeded expectations. Khudobin's stats took a massive bump over last season. He won't play in a minute of the postseason, but hopefully his effect is making Rask able to be healthy and ready, and that's the effect you hope your backup has had once you get into the playoffs.
That being said, Heinen, McAvoy, DeBrusk and to a lesser extent Grz, Schaller, Riley, and Krug have all had step-up seasons that exceeded their expectations and I would have been ok with any of them winning as well.