No, they aren’t. There is some overlap between “libertarians” and groups from left to right (in the modern sense) that are grounded primarily in classical liberalism, and those include the bulk of what tend to get labeled “libertarians” in America (which are mostly the center-to-right subset of the classical liberal subset of libertarians.)

But “libertarian” also encompasses anarchists, libertarian socialists, and a number of other left-libertarian ideologies that are not particularly grounded in what would usually be regarded as classical liberalism (most of them are grounded in newer philosophies which could reasonably be viewed as later developments from or reactions against – but not in a reverse direction – classical liberalism.)

In America, the word "liberal" in 1900 is very similar to "libertarian" in 2020.

You may agree or disagree with this variability (I'm not a fan personally). But there you have it.