That doesn’t seem contradictory to me. You need to be in a heavily obscured area or behind cover, which the second passage specified needs to be at least half cover.The playtest packets (which are kindly archived here) actually contradict themselves. I've researched each one, and the contradiction stays consistent from Packet 1 to Packet 10.
In the first passage, it outright states that you need to keep behind cover (not specified which) or stay in heavily obscured areas (VERY specific) to remain hidden. In the second passage, it outright states the thing must cover at least half your body for you to hide (VERY specific).
- "A creature can attempt a Dexterity (Stealth) check to sneak around, moving quietly and using cover and heavily obscured areas to avoid detection. [...] If a creature might see you, you need to keep behind cover or stay in heavily obscured areas to remain hidden."
- "You can't simply stand in the middle of an empty, lit room and hope to avoid notice. Something must conceal you, perhaps a large object, a piece of terrain, or an immobile creature of an appropriate size, such as a slumbering dragon. Regardless of what obscures you, the thing must cover at least half your body for you to hide."
That’s actually not far off from the published rules, though it’s a bit more generous in that it allows you to hide with only half cover. And in fact, it makes it pretty clear that, if a creature might see you, you need to stay behind cover or in a heavily obscured area, so moving into a lightly obscured area would seem to break stealth. Though IIRC there was a feat in some of the early packets that let you attack a target with advantage as long as you started your turn hidden from it. I remember cause I used it a lot on the rogue I played at the time.