Telling someone they learned something wrong maybe isn't the best approach when trying to explain why something should not be confusing. Especially when it's a widely held view, maybe the learners are not the problem.

Most people learn JSX when they learn React. It was created by Facebook for React, after all. What does the React docs teach about className?

https://reactjs.org/docs/introducing-jsx.html

Here in the intro it doesn't even explain that you need to use className instead of class. It uses it with no explanation. Then it throws in a line about camelCasing and assumes that you understand why it changed.

Surely the JSX in depth page explains it.

https://reactjs.org/docs/jsx-in-depth.html

It does even less.

https://reactjs.org/docs/dom-elements.html#classname

Finally! In a page that seemingly has nothing to do with JSX we get told to change how we write HTML, but we're not even told why. (The htmlFor section tells us.) No wonder people are confused.

Yes, className is a property of the Element interface but it is not the attribute used when writing HTML. You're still changing how you write HTML. It is no longer standard. That is the point people are making here - JSX introduces enough edge cases that you must learn that it adds equally as much mental overhead as the template DSL for Alpine or Vue. Even if people understand the reasoning and it is not confusing, it's still a shift.