The Official Forum - Question sub running onto floor during play

I was getting ready for the season (Middle school Official. I came across a Youtube video from a game in So CA. Serving team has an successful attack. The ball is about to hit the ground, R-2 pancake saves it. Serving team believes it was a down ball and the match winner. After the pancake save the ball hits R-1 in the lower leg bounces up and R-3 puts it over the net.
While this great save was occurring Team S begins to celebrate the win, not knowing the ball was saved. At least two subs (Team S)leave the bench and comes onto the court, while the ball was live. Team S returns the saved ball for a kill and wins the point, and the match. Score was 16-15 this made it 17-15.
The officials confer. They put both teams back on the court and give Team R the point 16-16. Team S then wins the match several plays later 18-16.
They never said what the correct call should be: Is it delay of game, or illegal sub? Thanks in advance. 'Im not sure, but I would like to get the correct call :)