Possibly exposed to high heat? I know this will sometimes cause the clad layers to bubble up and separate. It would also explain the mushy, pockmarked appearance of this coin. If you are thinking there is a dime inside of this coin, that would be completely impossible. The clad sheets are produced separately, and then the blanks are punched out of them. There would be no way for a blank to get sandwiched in between layers. The clad sheets are bonded together using extremely high pressure, so anything between them would be flattened as well.
Keep looking though, there are lots of real errors and varieties to find, and this is a great place to learn what is worth something, and what is just a damaged coin.