It was Origin's example, not mine. However the point being made, I presume, is that in science one comes across physical concepts that are not substances and yet have existence, according to certain well-established theories.
Fields, of various sorts, would be another type of example.
So, my esteemed friend, you are not really in a position - given your avowed lack of scientific knowledge - to dismiss the concept of the metric of space being stretched, merely because space is not a substance.
I might paraphrase you some Hamlet: "There are more things in heaven and Earth, Dylan, than are dreamt of in your philosophy".