Good point, thank you for the clarification! Somehow I have always thought about showing the intent of keeping the data structure immutable when using const. I have changed it in the article. One more learning for me today :)
My experience has been that both the change in value/reference behaviour and the lack of total immutability guarantees when using a const qualifier on a reference type can be a source of bugs.
Languages like C and C++ distinguish more explicitly between value and reference semantics, and likewise between constant pointers and [mutable] pointers to constant data. To some extent that removes those sources of bugs, at the expense of having to write more explicit but verbose types like `const SomeType &` instead of `SomeType` all over the place.