Many libertarians identify as anarchist. Some of my favorite libertarian thinkers are anarcho-capitalists.
Anarchism is the idea that people can coexist without a central force to compel them. Lawlessness and voluntarism are tenants of anarchism. The contemporary bastardizing of the term is partially corrected by the recent documentary: The Monopoly on Violence.
https://youtu.be/XWAEKQjN-yM
Some libertarians are anarchists because anarchism might be fairly considered a mode, or form, of libertarianism.
Homeschooling brought me to voluntarism, the non-aggression principle (NAP), libertarianism, and anarchism. Howdy🤠