Certainly some "luck" was involved, just as when McCallie fumbled a kickoff and gave Riverdale an opportuity for an easy touchdown. The coaching decision not to "take a knee" could also be questioned.
However, the coach did not fumble the ball or throw the interception. The coach also did not give up 180 passing yards in the last four minutes of the game. Riverdale had plenty of opportunity to overcome whatever mistakes were made, but failed to do so.
To put a little more perspective on the came, despite the dominance of Riverdale's running game, the game would have been tied before the "coaching error" occured if you take away the easy touchdown resulting from the fumble on the kickoff. Riverdale's offensive performance in the second half was more impressive for its time of possession than for the numbers put on the board.
Riverdale got beat in a game it should have won. It lost because of its inability to stop McCallie's offense when it mattered. Learn from the experience.