The author is well-known and well-cited -- especially for introductory articles about using react and react ecosystem libraries. I think he wants to make it clear to anyone that happens upon or is recommended the article that the contents of the article are not 'required knowledge' for using the library.
I think this is reasonable for this author to want to emphasize. It's quite common for a beginner to make one of several reasoning mistakes that might push them away from trying something or push them away from something they were already using. The beginner who hasn't used a thing yet might think 'I need to understand how this thing works in detail before I can use it' in which case they might think reading an article like this is an appropriate way to get started. The beginner who has already started using a thing might think 'here is a good article about how the thing I've been using works in detail which I can't understand -- therefore this thing I've been using must be too hard for me to use and I should look for something else'.
I assume for popularity retention reasons, the author doesn't want to encourage either of these kinds of mistakes.
I think this is reasonable for this author to want to emphasize. It's quite common for a beginner to make one of several reasoning mistakes that might push them away from trying something or push them away from something they were already using. The beginner who hasn't used a thing yet might think 'I need to understand how this thing works in detail before I can use it' in which case they might think reading an article like this is an appropriate way to get started. The beginner who has already started using a thing might think 'here is a good article about how the thing I've been using works in detail which I can't understand -- therefore this thing I've been using must be too hard for me to use and I should look for something else'.
I assume for popularity retention reasons, the author doesn't want to encourage either of these kinds of mistakes.