Glad your buddy made it back. My parents' cat used to do this. He'd go away for a few days then he'd just be randomly sitting on the deck. My dad used to say he went on hunting trips because one time he had brought back a frog.
The only time he's done this before (twice) was on garbage day... when he gets out at night and gets stuck in someone's garage while they're putting out their garbage. Today was garbage day.