The managers I respected were all TLs who were the most important engineer on the project.
Going back to your point, the TL would be the best person to evaluate the engineers who work under them. 1:1s, growth discussions, etc should all be conducted with someone who knows your work intimately, which means the TL. Which means the TL is a manager.
There's still room for EMs to be more technical or more people/coordination-oriented. A technical EM would take responsibility for a smaller area (backend) and go deep technically into it, having the most impact as an individual contributor, knowing all the code, being able to debug any part of the system, being the go to person for everything in that area. Everyone in the backend would report to him.
An EM can also decide to be focused more on people/coordination. They'd take responsibility for a bigger area (backend, frontend, iOS and Android) and go wide rather than deep. If you ask them how to debug an iOS app that crashes in the background, they may not be the best person for that.
But in both cases, they're managers, not TLs.
The Technical EM is more about design, architecture and progress, and sometimes helping the team to get code out the door.
The Non Technical EM is more about this. The technical EM would communicate through a PR, say instead of having 1-on-1's.
Edit: They said in the article they used to give coding problems to engineering manager candidates, and then in the onsite interview, they found their managing ability is so far off of what they were expecting.
So they're making a shift from a Technical Managers to Non Technical Managers.