They are still a subsidiary of RBC Canada and are doing a CANADIAN credit check against your CANADIAN credit record. Opening a credit card at RBC USA using your Canadian details has nothing to do with your US credit history, nor will it contribute to one. It's not the same scenario at all. I don't get why people are failing to see this, it's quite straight forward.
To be nobody but yourself - in a world which is doing its best, night and day, to make you everybody else - means to fight the hardest battle which any human being can fight; and never stop fighting. -- E. E. Cummings