Libertarian anarchists have been right to claim "anarchism" as their own, since that actually is what they preach.
A great many people are genuinely confused about the history of anarchism for the same reason that people would be confused by me if I took a fervently pro-gun stance that I called "pacivism," and I think genuine confusion is also what motivates the re-purposing of the word. Libertarian anarchists genuinely don't understand that "anarchism" is like my "pacivism" example.
I didn't even understand that until recently, and I am pretty well-educated. I was genuinely confused. "How does Noam Chomsky's position ultimately equate to not having government or power?", I kept asking myself. I couldn't follow his logic. Then I realized, oh, he's not making that argument, and none of them are. Some of them pretend or actually think they are (due to their own confusion), which adds to the confusion.
Someday we will probably have the same problem with "progressivism."