But the language itself is still Smalltalk with some extra classes, right?

Smalltalk is just a simple meta-language (like Lisp and Forth). In your system, you may have the same or very similar syntax and keep some degree of compatibility but be very different in many practical aspects. For example, Pharo has Collections API very similar to Smalltalk but very different Files API or UI API. It has another class building strategy with stateful traits, slots, some syntax extensions, different source files format etc.

Kind of. At the very least you get traits, dynamic array literals and such that you don't get in "classic" Smalltalk.