When panic sets in, there is no telling what someone might do. Maybe they just hit send and their phone called the last person that they had spoken to or it's possible since they were "far out" they thought a friend could call and guide help to them faster than they could explain to 911. Do they have 911 out there? There are some rural areas with no 911 service. Who knows. This is very sad.
Last night I heard that the pond was "only" 12 feet deep. If this wasn't a huge body of water -and - if they could have gotten out of the vehicle, they may have been able to swim to safety.