The migrating turtles were almost certainly a cooter or slider leaving a drying pond or lake.
As for folks not realizing that they have turtles living near them I can relate to that too. I once found a promising bog in Virginia that I just knew had bog turtles in it. I asked the owner if I could walk around in his cow pasture and look for them. He said sure but he had lived there for thirty years and never seen a turtle before.
I found two bog turtles in a half an hour! On my next trip I found five in one hour. But the owner had never seen one in thirty years.