In-game just means In-engine right?
Maybe there’s a distinction I’m missing
So there are 4 levels.
CG - We know what that means.
In-Engine - Meaning it was rendered in the game engine but done so in a way that will not be replicated in the final product. Pretty much always because the consumer hardware can't pull it off in real-time. These always looks better than what you actually see in the game.
In-Game - Meaning the game will look like this in many instances but not necessarily always, depending on what is being shown. The game is capable of being rendered this way in real-time on consumer hardware.
Gameplay - What the game actually looks like when you are in control of the character. These last two can be one and the same depending.
The last two can and have looked better in trailers only to eventually be downgraded for varying reasons. But until release, there is no reason to believe they won't achieve that.