The rule is that if the opposing player (Nashville's D in this case) is the one who puts the puck in the zone, even if the attacking player (Duchene) isn't in yet then it is not offside, but it can't be banked off of them. If the Nashville defenceman there made a kicking motion, but just had it go off him wrong, then that was actually the right call. In the replay I see it go of the D-man's foot, but it's unclear whether it was a kicking motion. Maybe the linesman saw something from that angle that we can't from the replay. But even if it was the wrong call I'd guess that that's where his head was at in not calling the offside.
EDIT: Damn, beat me to it. My logic was right though. Woot.
Edited by Kyosama, 18 February 2013 - 06:12 PM.