I assume he made a duplicate thread that was also deleted eventually.
That’s exactly what happened.
I don’t think so. He already posted an explanation of what happened, and while he could be pulling our leg he is correct that it has happened before. If the OP has his post deleted then the next post becomes the OP and thus is listed as the author even if they weren’t. I don’t remember any details about the thread or who the posters were but I am certain I remember it happening before.