Someone scraped some public profiles. Someone then brute forced a poorly implemented "look up by phone number" feature. They linked the two datasets on the unique facebook user id.
Leaking data that is or was in the public domain is not much of a leak. The only noteworthy thing would be the leak of the non-public phone number, however that vulnerability has been widely known since 2019 (and has been resolved by Facebook), so there's nothing new here?
Where could I, or any Internet user, trivially download these details on 533M Facebook users prior to this dump? If nothing else, it seems extremely noteworthy that someone was not only able to obtain the data through scraping or some attack, but has shared with the world.
On Facebook. Literally. You can scrape any public profile info. It's against ToS, but it's not illegal (some caveats apply, see the hiQ Labs v. LinkedIn case for more info).
The only noteworthy thing is the phone number vuln. Except that's been known since 2019, so it's certainly not news.