The Pens scored and "it" was noticed, protested. The play leading up to the goal looked like an offside. The ref went to the booth, looked at the tablet and watched the play. After reviewing the video material he turned and skated to the center face-off circle. The mic: "After review, the play was offside. No goal."
Actually: no need. The referee just needed to turn, puff his whistle and point to the face-off circle at the Nashville blue line. Drama.
The National Football League adopted the officials' on-field announcements for a big reason: That league's rules are so thick and convoluted. (For some strange reason, few souls, if any, know the NFL rule book's full thickness.)
Ice hockey plays to a much more basic rule book, which is why it's a beautiful game. Just not the NHL's version....