1944 Mercury Dime Question About Error

So I was just rummaging around in my closet the other today whenever I found a binder full of foreign and old coins that I had found over about 15 years. In the binder, I found a 1944 Mercury dime. Only thing is, the entire other side of this dime is missing the classic reverse side to it. Instead, it is just completely smooth and without the rim. It doesn't look to be ground down, but I just want to get a second opinion as I know that some coins are just ground down for kicks rather than it being an actual error where two coins are put into the press at the same time. If this error is actually legit, then there I another 1944 Mercury dime with only the reverse (which is really cool to think about). Pictures are below, thanks.