Its because you can get some data if you opt in to relationship tracking. For instance, my 23andme shows like 1,500 genetic relatives. So saw you are jewish and opt-in to this feature. The person can login to the account and see X amount of other jewish people and their names. This is the data that was stolen from my understanding. Not the actual raw DNA of those individuals. With the current gaza/israel issue, you can see why someone having a list of the names of thousands of Jewish people might cause some concern.