I think there's a confusion between "sleep", where you're in bed but still awake, and sleep as in actually being asleep. This is specifically called out in the

I think there's a confusion between "sleep", where you're in bed but still awake, and sleep as in actually being asleep. This is specifically called out in the article where it says "if you’re in bed for eight hours, a healthy sleeper might actually sleep for only about 7.2 hours."