Having a 10% chance and getting it is the definition of luck. Again, it's not just the shot but the entire play. Not all shots are on target, not all shots get through, and Severson was lucky to get the rebound off of his previous blocked shot. The puck trickled in, but with just enough velocity to cross the goalline with 0.4 seconds. So 10% would be lucky enough, but really the odds were even worse than that.
You are beginning to sound like fellow Sens fans against the Rangers in the playoffs, where apparently it wasn't lucky when Pageau scored a late game-tying goal when the puck deflected off of his leg after bouncing off of two Rangers. Nothing lucky about that!