Does the customer have to create an account before ordering from a Google order link?

Not at the first step. Google's rules say the first step must not require sign-in, and the link must go straight to the orderable menu.

• The link must let the customer finish the order without a phone call or another site.
• Payment details must not be asked until items are in the cart.
• In some countries ordering options show under an Order online button.
• In others, Place an order links may show separately on the profile.