it’s $50 rather than $60, so maybe 160 pages instead of 200. I am not sure how they will fill that with just crunch, they certainly won’t be able to with what they mentioned so far.
An adventure can contain a lot less setting information that the previous big ones did, they served double duty as a gazetteer and/or introduced new rules.
The adventure will contain the maps, the adventure text, and the monsters. As you said it has to be able to stand on its own.
That does not mean that the other book cannot contain anything that benefits the adventure and that is not just generic crunch that could be equally used in any other adventure.
If the price points / page counts were reversed I’d say this is the equivalent to the Eberron book with Deadfall being close to a full adventure, just a tad shorter, but they are not. I am not sure there is enough crunch to fill 160 pages…