I noticed that same thing just this morning on my Indeed job search! Although I worked for Houston Public Library in the early-90s, I have been away from them all this time, so I can't really offer any up-to-date comments. I worked at Central as a Social Sciences Reference Librarian. The last time I spoke with someone who was working for HPL (about 2 years ago), he said that they were making extensive use of "floaters"--the librarians would have to cover positions at multiple branches. I don't know how accurate that is now. Maybe that's why they are hiring now. The Central Library underwent major--much needed--renovations recently. The job market for librarians seems to be good in the Houston area, right now (just the opposite of Chapel Hill area, in my opinion!).