Hi,
Well, that's also a guest form.
If you've activated the guest mode, then there is no HikaShop registration page, only guest form, even if it's named registration.
If you want a registration form page while you have the registration set as only guest in HikaShop you would have to use the Joomla user registration form page, not HikaShop's.
Alternatively, you can change the "Display method for registration" setting to "selector" in the HikaShop configuration and then select both the "registration" and the "guest" modes in the "registration" setting below. That will allow both guest and registration to be available on the checkout and your link will display the registration form of Hikashop.