While I agree with the bolded part, I feel that in the context of that section it is clear that they are actually talking about cover, not concealment. The previous two paragraphs describe half-cover and three-quarter cover clearly in terms of the portion of the target body that is blocked by an intervening obstacle.
That section would have been probably clearer if they just said something like "A target benefits from half-cover, three-quarter cover, or total cover if an obstacle blocks at least 50%, 75% or 100% of their body, respectively", but maybe they felt that read as too dry and they wanted a different style for 5e?