(Not to be pedantic but you can mutate objects without calling &mut self methods through reassigning visible fields, but I think I understand what you mean.)
Yes, but OwningRef/Value take ownership of the container and never expose a mutable reference to it. The only mutable access on it is deref_mut() (and technically, drop)
Anyway, if you have ideas for how to clarify the documentation, feel free to suggest them.