There's ample evidence that such kinds of speeds are not generally possible with every kind of book. See e.g. https://www.scotthyoung.com/blog/2015/01/19/speed-reading-re...
I did take speed reading courses myself. Sure, it helps you speed-read, skimming over sections that seem unfamiliar, and detect when you need to slow down, because the subject matter becomes too unfamiliar/new. I've also had the impression that retention improves a bit after the couple of training days - at least that's what the workshop instructor makes you believe (it's their job to sell success and good feelings so that you recommend the course to your peers).
In the end, I highly doubt that anyone who claims to have such high speeds is sincere. The simple fact is that marking text with a highlighter, making notes (with a pen) and thinking about the content (do you?) takes time. If you accounted for that and took the average, you'd get lower numbers. And that is fine.