Pretty much any of them. He interviewed zero HFTs for his book and seems to repeatedly misunderstand how the basic concepts of order books work, or things like

Pretty much any of them. He interviewed zero HFTs for his book and seems to repeatedly misunderstand how the basic concepts of order books work, or things like "someone trying to sell a million shares is going to drop the price of the stock", which you learn on level 3 at the very latest.