You're just factually wrong. The word 'libertarian' was first used to describe a political ideology in 1857 by the French Anarcho-Communist philosopher Joseph Déjacque specifically to differentiate his ideology from the mutualist anarchism of Proudhon.

The term 'libertarian' took off in popularity in France in the 1880s when the French government began to suppress anarchist newspapers. They just switched to using the word "libertarian" rather than "anarchist" to get around the censor. This is exemplified in the weekly newspaper founded in 1895 called The Libertarian (Le Libertaire in French).

The anarchists in the Russian Revolution and in the Spanish Civil War called themselves interchangeably 'anarchists', 'libertarians', and 'libertarian socialists'.

The term didn't come to be associated with classical liberalism and right-wing ideologies as it is today until the middle of the 20th century. It was a specific attempt by right-wing American political philosophers who held an allegiance to Locke-style 18th century classical liberalism, but felt that the term "liberal" had become too associated with left-wing (within the American context) politics.

Here's a quote from 1955 from the libertarian writer Dean Russell:

Many of us call ourselves "liberals." And it is true that the word "liberal" once described persons who respected the individual and feared the use of mass compulsions. But the leftists have now corrupted that once-proud term to identify themselves and their program of more government ownership of property and more controls over persons. As a result, those of us who believe in freedom must explain that when we call ourselves liberals, we mean liberals in the uncorrupted classical sense. At best, this is awkward and subject to misunderstanding. Here is a suggestion: Let those of us who love liberty trade-mark and reserve for our own use the good and honorable word "libertarian."

Here's a quote from the libertarian writer and philosopher Murray Rothbard from the early 1970s:

One gratifying aspect of our rise to some prominence is that, for the first time in my memory, we, 'our side,' had captured a crucial word from the enemy. 'Libertarians' had long been simply a polite word for left-wing anarchists, that is for anti-private property anarchists, either of the communist or syndicalist variety. But now we had taken it over.

Here's a quote from Ronald fucking Reagan in 1975:

believe the very heart and soul of conservatism is libertarianism

Modern libertarianism in the context of American politics is synonymous with classical liberalism and conservatism (up until the MAGA movement co-opted conservatism and just made it synonymous with fascism). But in the US prior to the middle of the 20th century, and outside of the US until much more recently, libertarianism was synonymous with anarchism and was very much a leftist ideology.