I haven't sent out the survey to the customer but still there seems to a rating on the ticket. How is this possible?

We have recently refreshed our branding across our offerings and changed the names of our pricing plans. If you have signed up before Aug 9, 2021, please click Previous plans to view your applicable plans.
We assure you that this change will not impact your product experience, and no action is required on your part.

If you have enabled the satisfaction surveys, the customers would also have the ability to rate the closed ticket from the customer portal itself.

Please check whether it is enabled in Admin -> Workflows -> Customer satisfaction and toggle the survey off if you do not want this to go out to customers.