That's strange because google pay uses a gmail account. I think whatever address you have under the payment section for your google account is what appears under google pay so I don't think it was in google pay and more it was already associated with your Gmail account which means someone who has access to your Gmail account had to have had set it up.We bought our Pixel 5 new from our carrier. When we went to set up Google Pay and add our credit card, someone else's address was already in the address field. Thoughts?
Edit, the address points to a hotel . . .
Is it possible you ever filled out an online form and used a hotel address rather than your true home address to avoid getting junk mail? If you had Autofill turned on, Google might have remembered that address.
Check your saved autofill addresses and see if the hotel address is there: https://support.google.com/chrome/answer/142893?co=GENIE.Platform=Android&hl=en