The trash bags that came from the tow yard office were black, the white bag could not be somehow confused with the garbage that came from the tow yard.
Well, partly. No one said anything about them being confused, because black trash bags with red handles look nothing like a white bag with yellow handles; just so we are clear.
What was in the bag that could have attracted blow-fly larvae? Not pizza, because there was no pizza in the bag. Blow fly larvae do not live for a month. Don't you find that odd? What possibly could have been in that bag?