Indeed this conversation has happened before.
https://geekhack.org/index.php?topic=64783.0It was even on the same listing!
It was concluded that the board was probably refurbished in 1996 and the internals are the original 80's vintage bits. The label is incorrect, but likely just through error.
The workers might not have even known that a Model F line existed, so they just stuck an M sticker with the right part # on it. Maybe it would be a hassle to add Model F into the label making machine for such a low number of these boards moving through. Who knows, but it's not like the eBay seller put the sticker on to try and fool anyone.