No, what Backes did in the Stars zone was fine. As Oleksiak shot the puck after the draw, Nichushkin tried to skate to the net but the Blues defender stuck his arm into him and skated backward into him, blocking Nichushkin's path. It's clear that the defender isn't playing the puck since he actually removed himself from the shooting lane in order to interfere with Nichushkin. Nichushkin tried to cut around the interference but he fell to the ice. The rebound came to an area where Nichushkin would have been nearest to the puck if he hadn't been interfered with. Instead, the Blues pick up the rebound and went down the ice and scored.