i seen that trick before...sounds like he pulled it off on you too...he was prolly sober as you, but power of suggestion got him out of your yard without a shot being fired...
you've been tagged...
hard telling if he will be back, but its an old rippers trick to act drunk, come messing around your back door area just to test out what response they will get, before making entry, and robbing you blind...
crackheads only understand what no tresspassing means when thier picking birdshot out of thier backside!
i would set up some security on that back door area myself, even if its a dummy cam with battery operated light, or a driveway sensor to warn you.
favor fortunes the prepared...