Not really sure, I know they are matching your address, phone number, and name to your credit report and then if you accept the offer (if i can remember) they then confirm your ssn and d.o.b.
Also, when you go into some stores this happens as well sometimes. Sometimes, if they have ran your card ( i think credit card, but could be debit also) through their system and they ask if you would like to open an account, this could mean they see a preapproval popped up on their screen for you. Sometimes they just ask everyone before you start to check out.
Also, sometimes the sun needs to be shining just right…I say that to say again, everyone’s situation is different so you may get different results.