Vedanta claims that the universe is in your mind, and nothing but your mind. He says this world which you are seeing here is not a creation of your mind. You have not created this world out there. Eris no time to discuss that. What vedanta is proposing is not subjective idealism. Subjective as idealism is a philosophical position which states that whatever happens in your dream was all in your dreaming state. But shanka attacks the buddhists because he wants to distinguish his position from them.