Yes, that is because an 'investment' in the economy money is the same as an 'General Investment' in the entire economy. Think of it as a weighted basket investment in every venture in the entire economy... That is what money is.
That statement is very interesting. But note that is only true for a fixed money supply and no hoarding.
If I were able to hoard 50% of the money supply for a long enough period of time, the other money owners would have a 50% return even with no growth.
When I release the money by buying goods and services, I will enjoy the same return at first, but less and less while inflation occurs due to this money release.