Good feedback can also be taken to mean solid critique, especially if contact with the customer has been intensive and involves a complex result. What typically happens in these cases is that the manager or an account manager reviews the project after it is done (and depending on the duration also at regular intervals with the client) to verify if the client is satisfied and whether some things could have been done better (and to pave the way for future sales). The information from such reviews if the contract went well is typically rather vague.
A problem with your current replies is that they stop your new manager from progressing into an exploration of the feedback with you. Your new manager does not know you yet and quite a few managers have been promoted/appointed on the basis of other skills than social skills. Note also that the manager gained this information second-hand (from the customer) or even third hand (via an account manager). Enter the awkward silence, he may want to talk about it further but does not want or know how to take the initiative.
So, if you dare, open it up and say:
Thanks, but I am sure some things could have been done better?
This invites him to suggest improvements based on the customer's feedback. But be prepared for a follow-up such as:
What would you suggest?
And then you can suggest a process improvement. There is always something that can be improved in the process. Keep away from negatives and motivate.