The great-grandparent comment was talking about an "information density limit" and black holes in our universe, so I assumed the referenced sci-fi collection had something to do with holography. I don't know of any particular emphasis on AdS in that context before 1997. Elaborate?

Obviously you can stick GR in AdS, but AFAIK nothing about that would've seemed interesting with regards to holography before Maldacena, let alone plausibly providing inspiration to a fiction author.

To be less roundabout than my previous comment: I think Baxter may have been inspired by the holographic principle in general, but I doubt AdS crossed his mind at all when he was writing these stories in the 80s and early 90s.

(EDIT: or maybe Baxter was thinking about AdS but not about holography. I haven't read his work.)