I think they mean it’s similar to a one-way hash in that you can verify that the interference ‘fingerprint’ of someone when you see that pattern again, but you can’t identify a person from only the interference data, so for instance you could have a database of targets to locate, and share their wifi fingerprints with various other agencies to monitor for, without actually sharing their name, image, etc.

Obviously surveillance as a general concept is inimical to privacy, irrespective of how it’s done.