The article mentions that Hurd is also a recursive acronym, but doesn't go into any more details.
After looking it up on Wikipedia, I see why not:
It's time [to] explain the meaning of "Hurd". "Hurd" stands for "Hird of Unix-Replacing Daemons". And, then, "Hird" stands for "Hurd of Interfaces Representing Depth". We have here, to my knowledge, the first software to be named by a pair of mutually recursive acronyms.