Does OAS3 callbacks also relate about the Service implementation part ?

Does OAS3 callbacks also relate about the Service implementation part, because if at all this callback endpoint might be a part of different Swagger as well ?

Lets say I have OAS3 based Swagger101.json that has a subscription endpoint operation which is configured with a callbacks operation for callbacks URL.

So does the callbacks definition for this mean that the callbacks URL belongs to some other Service Swagger spec or basically another Swagger JSON. There might be a possibility that this callbacks endpoint operation might be part of whole different Swagger spec that has a lot of operations and endpoints to offer.

Does this make sense ?