No, you don't!
After completing the checkout (clicking on "submit order"), if the preferred payment option you chose is "paypal", you will be directed to paypal's page which allows you to either login and pay or pay by credit card without opening an account.
Please take special notice, paypal didn't make an effort to emphasis the option to pay with card without opening an account, but in the middle left of the page, you'll find the link leading you to the payment form.