Surely what they are saying they are doing is not really possible. They cannot with certainty verify who is paying who. They might be able to make probabilistic statements, but not certainty in all cases.
Even probabilistic data is bad. They could use it for targeted advertising for instance.
Plausible deniability is not the be-all and end-all. Even if they don't know for sure it could be reason enough to put you under further surveillance.