I concur. The vast majority of people have the exact opposite problem and sleep too little, therefore the general advice would be to get at least 8h of quality sleep per night.
It threw me off the whole article as well, it's hard to take it seriously when it hits me with "don't sleep too much" in the beginning, especially since I've always been somewhat of an insomniac and I'm intimately familiar with the impact of sleep deprivation across all aspects of one's life.
They do mention that sleeping too little is also a problem. Sleep varies so much from person to person that it is often controversial. It might be better to think of that point as advising you to try to optimize the amount of sleep you get. That's more of an experimental process where you find out how much sleep you need and how to get it i.e. what do you need to change in your life in order to sleep better.
It threw me off the whole article as well, it's hard to take it seriously when it hits me with "don't sleep too much" in the beginning, especially since I've always been somewhat of an insomniac and I'm intimately familiar with the impact of sleep deprivation across all aspects of one's life.