Corporations do not possess the kind of authority that is used to define authoritarianism.

US libertarians or the people who call themselves that are a different breed, it doesn't really matter what those authoritarians want to call themselves. I mean they're also calling themselves patriots and we know that isn't true.

Just like how US liberal democrats are barely centrists instead of the leftists they pretend to be or others call them.

Another problem with this grid is that authoritarian and libertarian are both loaded terms and not opposites of one another.

Many people take "libertarian" to mean unfettered laissez-faire/neoliberal capitalist economics - which is a fundamentally authoritarian so long as people within those structures depend on wages and insurance plans for survival and are beholden to contracts; a CEO without red tape is therefore no different from a mini-dictator. Anti-authoritarian measures to regulate the power of corporations are also anti-libertarian. Laws which prevent corporate monopolization are also anti-authoritarian and anti-Libertarian.

The opposite of authoritarianism is not libertarianism, it's anarchism.

Historically, "libertarian" was a synonym for anarchism or the libertarian branch of socialism. In most places it is still used that way, and even in the United States where right-wing liberalism has appropriated the "libertarian" label to an extent that older sense is also still used. 

The first "libertarian" was Joseph Dejacque an early communist anarchist who used the word to circumvent anti-sedition laws in France which prohibited the use of "anarchist." 

I would say the workplace is a very important part of everyday life for many people so they do have the kind of authority on each of their microscales to be authoritarian. Hell they are authoritarian by virtue of their structure aka owner, board, manager, workers, etc. 

Again, not authoritarian by the political definition. This is about politics, not sociology or philosophy.

If you want to take it broader I could even say my hobbies are authoritarian because I would literally die from depression if I didn't have them, so they are commanding me to do them.

I think it is by the political definition. Economics and Politics are linked very closely