I have read it, and find it bullshit.

What exactly do you disagree with? It’s really just a definition. If you are encountering people who are advocating for authoritarianism while calling themselves libertarian, then they are misappropriating the term.

Libertarians always manage to decide to “strategically” vote for the Republican that promises authoritarianism but also promises low taxes.

This is very likely to be a faulty generalization. Also, there are policies on both the Democrat, and Republican side which can be construed as authoritarian.

Again, it’s not about what Libertarians say they support, it’s who they actually support.

I’d be very hesitant to call stategic voting “supporting”.