A few things.. If it was public land, theirs a small chance they were scared by the decoys.. slim chance, but could happen.. Secondly like you said, they may have got to the creek and said screw it, im not gonna cross the creek to get over there..
The only thing that has me wonering is this "pucking" sound they were making.. to me it sounds like they were alarm putting.. and this is most likely because they didn't like something about the setup... maybe when they got close they saw you or your dad move.. this will usually put birds into a half alert.. and they will putt likeyou said you heard... To me, I would say the reason they got up and left was the third reason.. they saw something they didnt like and it spooked them a bit, so they went the other way...