I notice the "Limitations" section talks about how content only at some point touched by Claude may return a positive, and content that returns a negative may still be Claude generated. But I really would have liked for them to state explicitly that entirely false positives where a piece is fully human-written may still be marked as generated, because too many institutions with the power to ruin someone's life over t…
I think that false positives are inevitable due to the method of watermarking being embedded in the text itself. The output is intended to mimic human writing, therefore it's entirely conceivable that a human could by chance write text that contains the watermark. The odds may be extremely small, but it's not something you could ever guarantee.
I think in this case I think it's some kind of cryptographic signature smeared across the token IDs, so I don't think the risk is very high.