Specifically the pools Casual Nudity and Artistic Nude.
I had assumed it was. So when I noticed a user adding many posts to these pools which (among other things) weren't nude I started pruning. When I realized I was removing far too many, I stopped and reverted my changes.
Examples:
post #7172093 (first noticed, topless + panties)
post #6902308 (camisole lift)
post #167799 (topless)
post #7164432
post #6636236 (almost fully clothed)
Conversely, and for reference, post #10452 has been in and out of both pools since they were created in 2011, despite technically not being nude.