Operator overloading is a perfectly reasonable feature in a language to make use of and to assume works. If it is not going to behave sensibly, it should be an error, not nonsense, because having it work for strings but not other sequence types is surprising, and surprising is bad.
As I said, the fact that you didn't know the result means that JavaScript's type system is opaque and hard to understand. You might have understood that there are some things you "shouldn't do" but being hard to understand is a bad aspect of a language even if it doesn't prevent you from writing correct, good code.
By way of analogy, thing of a language which, like JavaScript, doesn't require semicolons, but they are accepted. Except, if you use a semicolon after the last statement in a block, that statement never gets executed. Your reply is like saying, "just don't use semicolons - they're not needed" instead of acknowledging that an element of the language which is prone to causing mistakes is bad design.