It says "all objects of the same constructor", which can be losslessly translated to "all objects with the same prototype that were created using JavaScript's retarded way of trying to look kind of like a class-based OO language when really it's not at all".

If you change an object's prototype, that object is no longer "of the same constructor". "Ninja.prototype = { 'swingSword' : ...}" is, in fact, a completely different, far more dramatic action than "Ninja.prototype.swingSword = ..." You shouldn't at all have the expectation that the two are anything alike.