Yes, in this conception of what it means to dispatch on the actual returned type, the caller doesn't know, in the same sense that it doesn't know what sequence of methods is dispatched based on the arguments, either! It calls a generic function, which does some magic internally and produces a return value (or various side effects or both).

By the way, it appears I can explain why I had used the word "fantasy": I have been recently involved in some discussions about Gödel's Incompleteness Theorem. That stirred up distant memories of reading Hofstadter, dredging up some of his vocabulary.