Base runners advancing two bases on a dead ball?

The other team had players on first and second. The batter hit a fly ball to deep right field. The right fielder caught the ball and the man on second started to run, but when the fielder threw to third, the runner turned and ran back to second base. The throw was over the third basemans head and went over the fence by the dugout. The umpire advanced the runners Two bases. They went from first and second to third and home. I thought once it is a dead ball, the runners advance only one base. They said something about the one plus one rule. I've never heard of this. Anyone know of this rule in highschool baseball?