Yeah, I am in wonderment too. The play was just like the one in a Wild-Blackhawks game where Parise appeared offside but was called onside.
I think the refs are Overthinking It. The rulebook doesn't allow an exception to offside for this situation. To the contrary the rulebook seems to me to clearly define it as solely based on where the player is when the puck completely crosses the line.
(From the 2015-2016 NHL rule book. Couldn't find the 2016-2017.)
Rule 83 – Off-side 83.1 Off-side - Players of the attacking team must not precede the puck into the attacking zone.
The position of the player’s skates and not that of his stick shall be the determining factor in all instances in deciding an off-side. A player is off-side when both skates are completely over the leading edge of the blue line involved in the play.
A player is on-side when either of his skates are in contact with, or on his own side of the line, at the instant the puck completely crosses the leading edge of the blue line regardless of the position of his stick. However, a player actually controlling the puck who shall cross the line ahead of the puck shall not be considered “off-side,” provided he had possession and control of the puck prior to his skates crossing the blue line.
It should be noted that while the position of the player’s skates is what determines whether a player is “off-side,” nevertheless the question of an “off-side” never arises until the puck has completely crossed the leading edge of the blue line at which time the decision is to be made.
If a player legally carries or passes the puck back into his own defending zone while a player of the opposing team is in such defending zone, the off-side shall be ignored and play permitted to continue.