If you’re referring to the guy hitting a metal rod and then using it to ignite a peice of paper, 2 things:
1) Compression generates heat. Every time the rod was struck, it compressed slightly, which increased the temperature.
2) Even if there was no compression, in pretty much every non-perfect physical interaction, some energy is transferred into heat. Hit something hard, fast, and constantly enough and it will raise in temperature significantly. You can simulate this yourself; Rubbing your hands together is essentially just hitting them over and over, and it very quickly warms them up.
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