I don't think it's a memory thing. The original rust compiler was written in OCAML. I think it's closer to an ML personally because of the strong focus on the type system rather than the chr* magic of c/c++.

Over the years c++ has been influenced to offer things people like from rust. So modern c++ looks a little more like rust. But older c++ really doesn't.

Similarly rusts approach to dynamic dispatch is more like OCAML than c++.

You can use rust and c++ for similar objectives though. Anyone can reduce two technical things until they are identical or expand them until they are completely different.

I think the most sober take is they are sufficiently different from one another.