Military uses lots of tracers rounds, exploding shells, and steel core penetrater rounds, they all can start fires. Shoot a steel core at a rock and you can make hot sparks. Hit the rock with lead or copper and you may be able to get a cold spark if everything is just right.
To create a hot spark you have to peel off a speck of steel and heat it up to its ignition point. The burning steel provides the energy to ignite the tinder. The impact provides the frictional energy to ignite the steel speck as a hot spark. With other materials you can also produce a cold spark that you can see but lacks enough energy to ignite tinder (for 'non-sparking' tools they actually test this by using carbon disulphide which is vastly easier to ignite than tinder).
If you doubt the OSHA, FS, DOD, and other scientists who study this then you should get some tinder, a rock, and some lead and copper hammers and see if you can get get a fire going. That its really hard to do makes logical sense since rocks are always falling off cliffs and banging into each other and yet you don't see the entire country ablaze because of it.
P.S. An interesting tidbit you learn in Wildland Firefighting school is that all fires are presumed Human Caused unless it can be proven otherwise.