Sorry to hear about your experience... but I suppose it wasn't all bad - Your neighbor came through. I suspect you guys will probably talk a lot more in the future.
your story got me thinking though... and I wonder what the chances are something like this happened:
Some other Autozone customer did an oil change, put the old oil in the Mobil-1 Jug, then brought it into Autozone and instead of pouring into the waste oil container, he just left the jug full of used oil in the back for some reason.. or even on the front counter. Later that night, a store employee saw it back there and, either absent-mindedly, or because he was just an underpaid, tired, or otherwise careless person, he picked it up and put it on the shelf, thinking it had been misplaced.
I know.. probably unlikely, but it COULD happen. I, myself, have brought used oil into my local Autozone and been told that the waste oil container was full, and I should just leave the jug on the counter and they would take care of it. Makes me wonder now if they really did "take care of it" or.. did something else with it.
... Oh, hey, look.. This is my 2000th post. Nice!