It’s not FOSS and I don’t see a way to review if what they claim is actually true.

It may be a way to just help to diferentiate legitimate human made work vs machine-generated ones, thus helping AI training models.

Can’t demostrate that fact neither, because of its license that expressly forbids sofware adaptions to other uses.

Edit, alter, modify, adapt, translate or otherwise change the whole or any part of the Software nor permit the whole or any part of the Software to be combined with or become incorporated in any other software, nor decompile, disassemble or reverse engineer the Software or attempt to do any such things

sauce: https://nightshade.cs.uchicago.edu/downloads.html