Not accurate. Due to how widespread facebook trackers are, it can identify you from the behaviour of others. People in your social circle linking to your content. People in your subnet using facebook services. People who hgave your phone numbers linking to your content on whatsapp etc. It's scary how easy it is for a massive corpo to remove anonymity from anyone if they want to.
Not really, the way you write, leaves a fingerprint itself, so with a little bit of AI it's possible to link personal/identifiable profiles with pseudonymous/anonymous ones.
that F*book scrapes this user's personal data from other random places (very illegal)
and that they change the FB profile without asking the user specifically (should be illegal, but maybe they find an excuse in their terms & conditions)