That docs page is so out of date it’s pretty much useless. I wrote a post about this nearly a year ago and all of the problems are still there: Docs page for World Partition HLODs seems to be extremely out of date
It will build HLODs for landscapes. With mixed results.
The only way to use world partition with HLODs right now is to figure it out by trial and error. I linked some posts in that thread which might be helpful.