The description sounds like a "popcorn hammer" sometimes also called a "popcorn cannon":
The US TV show Mythbusters did an episode on this gadget a few years back.
Essentially, it is a cast metal pressure vessel that is used to make popcorn/puffed grains. It can be used over an open flame, allowing street vendors to use them to create both an attention getting show and a salable snack (when caught into a bag).
With a popcorn hammer, pressure is built up inside the vessel during heating. When it is released, the explosive decompression causes all of the kernels to pop simultaneously. The popping plus the vessel decompression sends them flying.
High pressure devices that rely on explosive decompression can be dangerous. Pressure cooked popcorn / puffed grains do have a unique texture, but safety is the main reason you don't see home versions of these devices on sale at your local department store.
With most seemingly impossible videos from the internet, it's either fake or best left to professionals. This one is real, but not something anyone should try at home.