I had a cat that would get locked in the neighbors' garage or storage building from time to time and go missing for days. He would wander the whole subdivision.
Once we went to a party in our neighborhood several blocks away, walked in, and there was our cat laying on the carpet being pet by someone at the party. They said he had followed them in the house. They thought it was the owners cat. He just loved people and was terrible unfaithful. Cats are sort of the "if you can't be with the one you love, love the one you're with."
When they are young they can roam quite a ways away. I hope he comes back soon.