It is, sadly, a
Magician's coin and not a genuine mint error. In the top pic, you can see where, just inside the rim, there is a second circular line or ring; it's particularly noticeable just above the word "REG". This ring is the "seam" between the two half-coins. It is made by taking two perfectly ordinary coins, taking one of them and putting it on a lathe to hollow it out, forming a shallow bowl. Then, take the second coin and grind the side you don't want to keep all the way down until there's nothing left of the coin but a thin disc. Now, push the disc into the bowl from the first coin, perhaps gluing or soldering them together (though an experienced magic-coin-maker can make it fit so tightly, no glue is needed).
You can find some excellent pics of some (American) coins treated this way in
this thread.
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