Oh, I didn't argue BG2 wasn't its own title, I casually mentioned that it could have been called an expansion rather than a standalone title. There isn't necessarily some gargantuan difference set in stone y'know?
English may not be your native language, but you demonstrate very good command of it nevertheless. Certainly sufficient to register the fact that a standalone title, well, stands alone; and an expansion expands on a previous one. One can be played in it's own right. The other cannot. That's pretty much as set in stone as things get. But we digress...