Re: 'It's not clear whether he also has a FB account or whether he's a non-account'
"Why does it matter whether he's a member or not? It's personal data that they have collected about him.
From a technical aspect, if he's a member it should make it easier for them to extract and collate the relevant data."
I'm just thinking it terms of how this can play out. If he doesn't have an account FB can present a defence along the lines of "we don't know who he is". If he has an account this defence is less likely to succeed and if the case then exposes the amount of data collected off-platform it makes it less easy for them to defend against a subsequent claim by a non-account holder.