If we know the agent then we never put it in a passive form like in the above example. It works fine in English but sounds very silly in Finnish. Literally translated, we could say in Finnish: "Kuppi kaadettiin pöydältä kissan toimesta". But in reality, no one would ever use that kind of sentence. We would simply translate that to "Kissa kaatoi kupin pöydältä". So the word "toimesta" in Finnish does refer to the saying "by someone", but you would mainly see that being used in some extremely official documents, e.g. some political or legal texts.