Huh, that hit was definitely late, the guy moves the puck and then Gudas goes into him. It wasn't like he was in his tracks and Gudas just wanted to finish the check, he actively changed his course after Czarnik made the pass. And to those bringing up Rinaldo's hit on Couturier, this hit was at least as late as that one (if we're just focusing on the timing and not the consequences).
Did you watch the video posted just above your post? Yeah, he hit him in the chest, but that's because Czarnik was turning towards him. But he was looking in the other direction the entire time and Gudas saw that, so the fact that he hit him in the chest doesn't make it impossible for the hit to also be blindside.
It does not matter that he wasn't looking at him. He hit him square through the middle front of his upper torso. That in no way shape or form can be considered the "blindside". It is not the hitter's responsibility to let up or be aware that the guy he's trying to hit doesn't see him. It is the hittee's responsibility to be aware of the hitter. And if he is not, then hes going to get blown up. And that is part of the sport.