A good deal of that info has to do with preventing moisture problems BEFORE the slab is poured. For installing wood flooring for those who aren't pouring a new slab, the author recommends a "fluid moisture barrier" rather than a plastic sheeting barrier, but doesn't say much (anything?) else beyond that. Is he suggesting something like Redguard?

No, he's suggesting a trowelable moisture barrier, or a urethane adhesive. And only with engineered wood. Solid just has too many issues on concrete.

We had customers on a basement remodel who wanted wood flooring below grade. Slab from 1986. We used BR111 flooring and the urethane pre-sealer and a special glue-down adhesive. So far so good, since 2007.The smell of the sealer is hard to get out of your nostrils.
Casey