Best info I found on this is from the HS Baseball Case Book. The Case Book is an accompanying book to the rule book that describes how to apply the rules in certain situations.
8.4.2 Situation E says, "All bases are occupied with no outs when B4 hits a ground ball to F4 and R3 collides with him as he is fielding the ball. RULING: The ball became dead when interference occurred. R3 is declared out. If the umpire rules that F4 could have executed a double play, then the umpire shall declare two outs (the runner who interfered, and the other runner or batter-runner involved). If the umpire rules that only one runner could have been put out, then only R3 is out. No runs may score and all other runners shall return to bases occupied at the time of interference."
Sounds like he did not make the right call.