It would just seem odd to me to announce a slate of hero movies, have one of them not be related to the others, and not announce that is a separate project like they are with justice league dark and sandman.
We can go back and forth on supposition, but for now we just don't know. I'm not rooting against your hopes, I'm just saying I don't think we have anything dispositive yet.
I don't consider the announcement odd at all, because I don't consider the slate announcement to be- necessarily- a declaration of a universe- but simply DC Branded films that have greenlit... to the extent that they're willing to make an official announcement. Despite knowing Dark Universe and Sandman are in development, the WB hasn't made a commitment in the form of an official announcement yet.
Shazam was simply grouped with the rest because it's a convenient and logical place to make the announcement along with all the other media that was coming out.
For example, I don't think that Ninjago is necessarily going to be in the same universe as LEGO Movie 2 and we don't know if The LEGO Batman Movie is in the same universe necessarily, but nonetheless they're all announced together because they fall under the LEGO brand umbrella.
Or, when they talk about TV or Animation, they talk about all the announced projects together, simply because they fit under the same topical umbrella... not because they share a universe. They simply share a medium.
So Shazam shares a medium and a brand, which is more than enough reason to group it, and would make it weird to separate it out into its own announcement, even if it's coming from a different studio, which they also go out of their way to mention.