Anarcho-tyranny means a government that doesn't enforce any of the laws that protect people, only enforces laws that protect itself. So it's like the absence of a government in the sense that a government is supposed to be tasked with protecting people's life and property.
Well that's objectively poor phrasing, then. 'Anarcho-' as a prefix refers to Anarchy, which refers to a society being in a state of not having authorities.
You could argue that having authorities that abuse their authority to self-serving ends renders that authority illegitimate, but by the admission of Anarcho-tyranny's own proponents (as a theory), they still recognize the existence of these "authorities", and just contest the governance decisions made by those authorities.
That's certainly a bad government, but to call it anarcho-anything is just downright confusing.
If you want a real understanding of a word, look to its etymology.
Anarchy
1530s, "absence of government," from French anarchie or directly from Medieval Latin anarchia, from Greek anarkhia "lack of a leader, the state of people without a government" (in Athens, used of the Year of Thirty Tyrants, 404 B.C., when there was no archon), abstract noun from anarkhos "rulerless," from an- "without" (see an- (1)) + arkhos "leader" (see archon).
From 1660s as "confusion or absence of authority in general;" by 1849 in reference to the social theory advocating "order without power," with associations and co-operatives taking the place of direct government, as formulated in the 1830s by French political philosopher Pierre-Joseph Proudhon (1809-1865).