It's standard practice for Facebook and it's been for several years now. It's simultaneously a way to combat bots and a way to start collecting data about you in case you turn out to be a juicy real human. They want your pic and your contacts so they can start establishing your real identity and recognize you in pictures posted by others. If you don't help them do that you're worthless to them so they block you.

My mum was briefly banned on FB the other day and she's the most inoffensive person on the planet. This is an account that's maybe a decade old. They reinstated her account after she appealed so something seems broken with their banning system.

This is a serious problem I think isn't actually talked about enough. There is a 'ring of trust' on most social media now that in my opinion goes far too far; if you don't have enough algorithmically determined 'trust,' you'll be booted off without a way to appeal. Reddit shadowbans the vast majority of new accounts, but hasn't been able to cut down on spambots; Facebook by its nature needs ridiculous amounts of personal information but even then doesn't actually use it to assign more trust since bot-owners can supply generated information that's equally as valid; really all social media, especially if you do anything at all to protect your privacy, assumes you're a spambot first, then only lets you participate after you prove beyond a shadow of a doubt you might be a human. I understand we're already half way into developing a dead internet, but there's no reason we need to go full throttle into it by limiting actual humans from signing up past a certain point in a product's lifespan.