They are different things. One is the likelihood of having difficulty with sleep during the deployment; the other one is a survey of how many hours of sleep you get even when you're not deployed.
In this case, it was 72% of people who said they slept on a regular basis six hours or less. I know we would all like to sleep much less than we do so we'd have more time to do what we need to do, but six hours of sleep is cutting it short. It does have serious impacts on our functioning. Imagine how that is for service members who are exposed to different kinds of challenges.