People are specifically talking about the engine itself and not the tools used.

We wouldn't call humans creating a calculator "recursive self improvement".

I wouldn't call the harness an AI, but I might call a tool that plays a major role in creating another one like it "recursive self improvement." For instance in the industrial revolution a metal lathe and a milling machine were instrumental in creating the next generation of themselves. Same thing with a robot that is fabricated by similar (i.e. older model of the same) robots. All of them lead to exponential improvement.