Perhaps so. But a lot of them were not, at least by the time I got involved in the early 1980s.
And your observation is about the LP, which has always been a long way from being all libertarians. In 1977, Edward Crane split with the LP to found the Cato Institute, which has represented the "moderate" libertarian viewpoint for 25 years now. I'd defy anyone to describe the Cato Institute as "anarchist".
The point is that libertarians were never solely (or, I believe even predominantly) anarchists. The article equates libertarianism and anarchism, which makes it a silly piece of opinion, even in 1979.