Long story short, IRD are in damage control mode, saw that Facebook hashes the data, and hoped this meant they could spin it as anonymous. It's very, very not anonymous. I did some digging, which I put in another comment chain here: https://lemmy.nz/post/14206010/10952716

Basically, Facebook want to avoid having their customers break privacy laws for sharing data. Instead, the personal information like phone numbers, addresses, date of birth are hashed then compared against a hash of data Facebook already holds.

The idea is you aren't sharing personally identifiable data because facebook will only match data they already have.

However, the whole purpose is to match up a specific taxpayer to a specific facebook user. Not even close to anonymous, even if you squint and tilt your head.