Unless they purposefully produced hash collisions by truncating the hash, they've just traded one unique identifier for another one. The information they throw

Unless they purposefully produced hash collisions by truncating the hash, they've just traded one unique identifier for another one. The information they throw away is not very hard to recreate, you just need to discover an individual person again (provided that the MAC hasn't changed), hash it, and now you've got the hash->MAC mapping for that individual, and you can look at their location history.