Well said. Far be it from me to be a hair splitter! (Well, sometimes I slip up, but I hope I don't mind too much when a friend calls me on it!)
I think this is a case where there is very little agreement. To be sure almost all will agree that putting a frame around a piece of the world and snapping is OK, be it 'manipulation' or no. And I think most will agree that if you obliterate every form and tone and color, drawing in your own for all, that is too far and no longer deserves the name 'photography' whether you call it enhancement or painting.
Between the two extremes, though, virtually every position has its proponents. There truly does not seen to be some general social consensus to which we may cleave.
This is probably so, if it is, because nothing of importance is on the line. We must have definitions for violent crime, for society's sake. And so a general social consensus arises upon which we may base our law.
So, yes, one can in theory proceed on the basis of social convention, on the general idea that most people know it, roughly, when they see it.
In this particular case, though, I don't think that works.