Awarding Bases

[Spence]

Field has a temporary fence in the outfield.

Hit ball goes "through" the fence or under the fence.

Outfielder raises hands to show the ball is no longer accessible.

Is this an automatic ground rule double?

I ask because someone told me they saw a game where the umpire awarded the batter 3rd base based on his belief that had it not gone through or under the fence that the batter would have ended up at 3rd.