I realize that this is a bit of a jerk take, but it seems that the author's problem is less with GnuPG and more with his reluctance to be careful and read a little documentation. I still have the first key I made in 2001, when a friend and I decided to try the system out. It worked the first time for both of us, and we happily exchanged a few encrypted emails. And that was the last time I actually used it - not because it's hard to use, but because nobody uses it, and I don't need to send encrypted email to myself. For about 15 years I've had an X-PGP-Key: header on my outgoing mail, pointing to a file on the web containing my public key. Not a single person has ever used it.
EDIT: No, I remember once, a few years ago, somebody did send me an encrypted message using my public key, for no particular reason. It was an amusing surprise.
For me this fits the narrative. Encryption needs to be transparent to the user in order to become ubiquitous. I assume most people are actually reluctant to read the documentation. If the tool is not self explanatory or fully embedded in the tools people use they will not see any broader adoption.
It too managed to use the tooling. But I knew what public-key cryptography is and was aware of its general concept. I do not expect anyone in my family to be able to set this up. Not without putting some time into it. And putting time into it they will only do if I pressure them to do so.
So I would say: Yes you are correct that he could have read the documentation. But from a UX perspective I do not see the failure on the part of the user.
The opposite take would be this: If you need to read a manual that’s a clear sign the system is too complex to be secure. The human is the weakest link so a system that relies on humans being intelligent or careful is insecure. Humans are going to be dumb, sloppy and in a hurry.
EDIT: No, I remember once, a few years ago, somebody did send me an encrypted message using my public key, for no particular reason. It was an amusing surprise.