I thought about driving down to the other landowners house and making formal apology and letting him know it was a misunderstanding, and that had we known that we actually didn't have permission we wouldn't have been there in the first place.
Sounds like you already know what the answer is.
I had a similar occurrence a few years back. Landowner calls me in to do hog removal. I contact the next door neighbor, who happens to be a real estate developer. They give me permission to hunt. We make a few hunts out there and caught hogs each time. Then one day we get back to the trucks and find some notes on the trucks, saying if we are caught out there again, our trucks will be towed, and we will be charged with trespass. All I could think is WTF....
A few minutes later, a truck comes blazing up the drive. I take an EPIC ass chewing by the rancher that has the place leased... I end up getting his phone number in the course of my ass chewing. When we left the place, I gave him a little time to cool off, then I called him up. Explained that I was under the impression the landowner had contacted him about us being out there, and that I would have contacted him myself if I knew who he was. I never got rude with him, and stayed calm and polite the entire time. Next thing I know, not only am I continuing to hunt that place, but the rancher is now getting me access to his friends grain fields, as well as other ranch land in the region.
Hopefully something similar will happen in your case.
