Marketpress registration when checking out


I've got Marketpress Pro, and I have everything working as I would like; however, I still have a question. When I went to test the checkout function, there is a box. On the left, it says "Have a User Account?", and has text fields below for entering a username/password. On the right, it has a "Checkout Now" button. My question has to do with the user account section: Is this asking the user for WordPress credentials, or is it some kind of registration to my site?? I am not seeing anything on my site where someone could register as a user, which is why this is throwing me off...