This is how the play unfolded from the point McDavid started carrying the puck. IMO Keith had pinched down to hold the blueline and Seabrook had to keep McDavid in check so that #2 had a chance to get back into position. If Seabrook slides over and opens a hole for McDavid, make no mistake, Keith won't cut him off in time.
At this point what is the reality for Seabrook? He knows the man going down the wing is not going to steam in offside. He knows Keith is in a race to get back into position and he can't give up the middle of the ice.
As the Oilers gain the zone, Seabrook still has to respect McDavid, because Keith doesn't yet have body position. If Seabrook leaves room in the middle, McDavid can cut to the open ice Seabrook leaves.
Seabrook continues to prevent the pass with his stick right in position and McDavid and Keith is still in a vulnerable position where McDavid could just go to the net without Seabrook taking that ice away.
McDavid makes his move and look at the options he has. The team has to respect to two trailing men who are open as well as try to (in a split second) contain whatever individual play McDavid might make. He was lightening quick to turn and get that pass over, that is outstanding skating, balance and skill.
I do think there is something to the play developing from the Oilers zone.
Saad forechecked on Klefbom, who put it in the corner for Larsson. Toews is working on cutting off the boards and moving in on Larsson. Keith is covering Yamamoto. Seabrook is off camera looking after Maroon. Nobody (Panik???) is near McDavid. This is a situation where Seabrook dumped it in and the Hawks are trying to force a turnover, but Panik was playing it like the Hawks had possession. If Panik is closer to the middle of the ice applying pressure, then Larsson is probably forced to try to go up the boards and the Hawks maybe keep the play in the offensive zone. Keith probably should have recognized this and not gone in to hold the play in the zone either.
That's what I see when I look at the play.