Selling an $8 ebook is a financial conflict of interest, but having tens of thousands of dollars riding on the fluctations of cryptoassets is having "skin in the game", which is totally different.
author here - I can confirm that it is never not hilarious when bitcoiners, whose sole topic of conversation is the price of bitcoin in US dollars, can't think of any worse thing to say to me than "but you sell a book for money!!"