Well, it was a difficult thing to catch -- even now after viewing multiple angles, it's still not clear to me whether the clearing of the puck struck Sedin, so I wouldn't bet that the linesmen could catch it so quickly on the spot. The puck was already on the way upward (in terms of camera view) because it had hit the glass before heading toward Sedin, you can see it suddenly changes direction a split second earlier in the white space between the stanchion and Sedin.

It's a non-reviewable call anyway. The Sharks let Kesler stroll in untouched and be directly in front of Niemi on that tying goal, when they could have steered him out of the way. Douglas Murray didn't turn around and knock Kesler out of the way until after the tip-in had been made, so that was the bigger mistake than the controversy about whether it should have been an icing call or not.