advaita is not subjective idealism

I am trusting the explanation here 

In advaita, objects really do exist. Ishvara is the material cause, as well as the efficient cause of the universe. The point is that the substratum of their existence is brahman alone. In the case of Berkeley, however, the objects only exist in the mind of God, as it were.

So where idealism claims that all matter is an idea in the mind of God, advaita says matter exists independent of observer but the basis of all this matter and the obeserver is all God.