I am well aware that C&P means copy and paste

And that is what you have done, or at least the affect is such. Just because you have brushed on top of the original car, without copy pasting stuff back on top of the base doesn't mean it is C&P

If the piece is from the base, and un-modified, it's C&P, even if no C&P was conducted

ah, you get what I mean
However, that is my view of it, others may have another view of it, but since the effects are the same I think my reasoning is quite valid
Cheers!