Algorithm can identify 99.98% of users in supposedly "anonymized" data

Although the number of attributes is misleading, it helps lay people understand easily how it works.
I guess they are using something similar to this:
https://wiki.mozilla.org/Fingerprinting

Each of the attributes can separate the users, and some of them carry much more information and can discriminate more.
But, even the more inoffensive ones can be enough when combined.