This happened to me once a few months ago. I went to my local post office, it turns out they have something that captures the GPS location of the mail carrier when they mark it as delivered. So they said "oh whoops this was accidentally delivered to X address instead", the carrier went to that address, left them a note, and in a few days I got it back
plausible; a package from USPS was delivered a while after it showed up as delivered online. If the package doesn't show up in a few days, then it probably got stolen.
What probably happened is the person who actually received it turned it back do to incorrect address