Secondly, this analogy holds true in many ways; have you ever tried learning a new language?If your vocabulary is limited in a language, then your speech will also be limited.Also, you won't be able to write anything down.
Again, you can start banging on the piano, just like you can start yelling jibberish and call it Spanish, but the analogy works.
Plus, "improvising on a high level" doesn't mean anything.