The purpose of this component is to provide a UI to display text on so you could display this as a "script" (script like what an actor or actress would use) that a user would read from to their customer. The "script" (script like short snippet of code) component allows you to write your own C# code to do whatever you like. I don't believe I've ever used the "call script" component ever (over fifteen years).
It certainly seems like you have found a bug in the component. If you have a use case for it, then I would recommend that you open a support request to have it looked into. It might be just as easy to create your own UI to display a popup with whatever text you want though.