The consensus on the MD forums is that it's a game piece, but I couldn't find anyone outright posting a nice clear pic of the game-piece-coin and saying "Here is the piece from the game, as you can see its exactly the same as our mystery piece". I also note that several different pirate-themed board games and information packs are alleged to contain one or more of them.
All I can say for sure is, there isn't a genuine old coin with this design. So if they're marketing these as "replica pieces-of-eight", they're lying. I think we can also say, given the sheer number of them that turn up here and elsewhere, that they are or were mass-produced.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis