They always hard pull in the end with your consent before they seal the deal. Pre approval ... is one of the permissable purposes... where they research a bunch of ppl's credit report's for advertising and pre approve the ones that they are willing to extend credit to. However they can only see a snapshot of your credit as of the time they did the pre approval search. They will also do a hard pull when you apply through the pre approval to see if anything in your history worsened since the initial soft pull. Advertising or pre approval is always a soft pull. If you take the offer, you should expect a hard pull before they extend you credit.
I believe in your case they may have did a pre approval inquiry for all of their members and you passed their qualifications for credit lending.
