I don't know much about doggie perception but I certainly find it interesting how they can find their way home over long distances they are completely unfamiliar with.
I guess one possibility could have been your friend may have told your dogs you were coming home that day and they picked up something good was going to happen in her voice and put two and two together when they heard the car pull in? Who knows lol. I guess there could be plenty of other explanations also.
I know once I had a cat that hated going to the vet. I don't care how non-nonchalant and casual we acted on the day of the appointment, somehow that cat always knew and stayed under the bed until it was time to pull him out to put him in his carrier.
It was the darndest thing. We would be very careful not to make any reference to the appointment or say or do anything that would tip him off he had an appointment that day. It did not matter, He ALWAYS knew. lol.
That's awesome. I think we give animals that share our lives less credit than they deserve. You must have acted differently dispite your efforts and the cat knew it.