TheBigD5er

Have a weird situation that happened to my team recently in a high school game. my team is hitting. down two runs. top 6. runner on first, one out. hit and run is on. runner gets a great jump and has rounded second by the time the batted ball clears the infield headed towards third. Left fielder commits a fielding error and the ball goes rolls past him and goes through a hole in the base of the fence, becoming a dead ball. At the time, the runner from first is halfway home, the hitter is in between first and second. The umpire leaves the hitter at second, and brings the runner from first who almost scored, back to third base. He explained that situation is treated as a ground rule double, and each runner gets two bases. My argument was it wasn't a ground rule double. It was a single, The fielder made an attempt on the ball, committed an error, and the ball went out of play under the fence, not over. Based on when the ball was declared dead, each runner should receive two bases. (baserunner scores, hitter at third). The field umpire deferred to the home plate for the ruling. What is the correct ruling here?