Yeah, I've seen that many times before. The tire is so dry rotted that it's separating from the inside.
Pull the core out of the valve stem. It could blow just sitting there.
This happened to me. Monte sat in the garage for a few weeks when I first brought it home. Came home from work one day and the tire had blown up and tread and wire were all over the garage. Those tires were beyond tired, even sitting in the garage.