Can you share which parts made you think that? I don't think that's a fair assessment.
I was unexpectedly appointed manager
Presumably you were either on the track for management or agreed to accept the position in lieu of some other sort of transfer or lay off, much like the person in the article. Management isn't for everyone, but nothing in the article sounds out of bounds for a normal management job and 21 reports isn't really a lot.
I have had as many as 15 and after 10 you really just have to start picking what you want to fall off of your plate as a manager. Unfortunately, the things that fall off first are the things that help your direct reports the most. Eventually, you just get behind on everything and end up being completely reactive and only able to focus on short-term solutions.
21 direct reports are a lot if you want to be a good manager and support your people.