This seems to assume a very specific point of the GM's notes: to describe imaginary events which will occur in the fiction. AD&D 2nd ed modules are full of notes of this sort.almost every GM I play with, we talk shop. We discuss what the original plan was, what the original encounter was, how things were altered, where it came from, alternatives they had in mind but didn't use, etc.
As @Ovinomancer said, there are other RPGs that don't use this technique at all.