Assuming you don't store the salts, this produces a value that is useless for anything but counting something like DAU. Which you could equally just do by counting them all and deleting all the data at the end of the day, or using a cardinality estimator like HLL.
That same uselessness for long-term identification of users is what makes this approach compliant with laws regulating use of PII, since what you have after a small time window isn't actually PII (unless correlated with another dataset, but that's always the case).
That's precisely all that OP is storing in the original article.
They're just getting a list of hashes per day, and associated client info. They have no idea if the same user visit them on multiple days, because the hashes will be different.
