It's probably just a line in a database with your email address and phone number. It's not like Facebook is actively keeping tabs on people that don't have accounts.
The profile also probably contains a list of all the Facebook users who had you in their contact lists, and all the photos that you were tagged in. Since such information would get updated every time a Facebook user uploaded your contact information or tagged you, I'd say this qualifies as Facebook actively keeping tabs on you.
How do you tag someone if they don't have a Facebook account? AFAIK it's not possible to tag someone with an email address or telephone number?
Certainly you can "tag" someone if they are not on Facebook and not in your friends (of friends) list, but it is then just tagged as text, not associated with an account... maybe I missed an option somewhere...
I would suggest that the noise from associating free-typed tags (subject to spelling errors and without a user account attached) with photos would be way higher than the signal you'd gain. I even have irritating friends that tag people who aren't even present in photos just because they want them to receive a notification about it. All of that is total garbage input to any machine learning model or otherwise.
It'd be easy when editing the tag for the server to say "Does this name match this user in the imported contact list? Yes? Ok, it's most likely that person then."
I have a lot of noise in my contacts list though. Very rarely do I have a surname, mostly it's suffixed with "home", "mbl" or "work" or even city name as surname sometimes. I'm sure a "best guess" would be possible, I'm not sure of anyone that religiously stores first/last name aside from pure business contacts.
With smart phones with keyboards and cloud sync I think more people are starting to. I do now, and have since 2008 when I started using a smart phone. I've noticed more people switch over from short nicknames to full names with easier input. It's easier than going to your contact and saying "who the heck is James?" Now I just keep as much data as possible on each person. That way I also have their address handy, in case I need to mail them something. I've been meaning to start keeping birthdays in there too, so I can get a notification on my phone.
I wouldn't be so sure about that. We know that FB works with third-party companies to track offline purchasing behavior of its users (data which is supposedly anonymized).
So, I wouldn't think it a far leap that Facebook might correlate non-member invitee e-mail addresses with, say, the activities/interests of the inviter. This could be happening right now for all we know, or it could happen in the future. Once they have the data, it's their choice.
It's probably just a line in a database with your email address and phone number. It's not like Facebook is actively keeping tabs on people that don't have accounts.