I agree, it sounded a bit silly.
It was actually my intention to say: a good book can help in studying the basics of any HDL-language. Usually, there are a lot of small examples that you can analyse in structure and implementation results.
Courses from Doulos, etc. have the advantage that you get professional advise.
At the end you are on your own in the mad (but exciting) world of programmable logic. And then it comes to practice.
Hope this explains the very synthezised phrase "Basic knowledge comes from courses and a book can help"
Regards,
L.