Maybe since it's close to the road someone blew a tire decades ago, it went air borne and there it landed. I have seen truck tires fly off in one piece and roll down interstate 78 in PA, bounce off another car and fly through the air, landing god knows where. Anything is possible!
I doubt it because the tire is not on a rim. Sure makes us think though. And you are right, I too have seen some tires go flying. Best if they are going away from you!