It’s only an advertisement
You didn’t get pre-approved, only pre-selected. It only means that you met their basic parameters to go on the mailing list for such offer.
If you read the fine print, somewhere it says something like “up to”, which means that if you don’t qualify for the offer, you could get lesser terms (lower limit, higher interest, no rewards). You could even be denied completely.
The Fair and Accurate Credit Transactions Act gives the credit bureaus permission to sell your credit history information to credit lending companies, which screen potential clients and put them on mailing lists.
When National Bank pulled you credit file, it generated a credit inquiry. If you pull your report you should be able to see their name in the inquiry section.
However, it has zero effect on your credit score. Although the (Soft Inquiry) appears on your file, because it was NOT initiated by your search for new credit, it is NOT considered by the Fico formula.
Consumers have the right to exclude themselves from receiving such pre-approved mailing offers.
You can tell the 3 major credit bureaus to exclude your name from lists for pre-approved, unsolicited credit and insurance offers by calling 1-888-5-OPT OUT (1–888–567–8688).