I'm not sure if what you said is correct, because if you want to expose a service via REST with spring, you are going to use a controller. What he might be saying is that you make a basic REST api to get only the minimum data from the service, and for the 'controller' you might have something more complicated that involves multiple services.
What are you trying to do?
Actually making a call to a rest api in a controller seems a bit insane. Correct me if I'm wrong, but the only reason I can think of doing that is if you don't have direct access to a service. I think maybe you misunderstood what the guy was telling you.