Allocation more or less everything on the heap (i.e. using the stack only for calls and returns) is something that's done out of necessity in exclusively GC'd languages, like Java or Python.
That was my first thought as well when I read that passage. Do you know why the author might have felt the need to state this specific in the context of Rust then?
Note that it only applies to local variables. If you have a primitive inside an object then it's allocated on the heap as part of the outer object.
I'm just wondering if the extra emphasis on stack allocation has created issues; this article doesn't cover the allocation of Strings or Vecs (wrapping them in RC and ARC boxes), and most other references on the net are a few years old now.
As in C++, these are small stack structures (a few words, IIRC it's 3 for Vec, and String is backed by a Vec) pointing to a heap-allocated buffer.