Schrodinger was talking about states not probability, However we can use probability to better understand this. If you are to pull a letter either a or b from a hat, and you reach in and select one of equally numbered "a"s and "b"s we can say that the letter in your hand is either a or b. The default position is to not believe the letter is a or b until you have some evidence upon which to base your belief. Conversely, we could describe the same probability by believing both are true, until we have some evidence upon which to base our exclusion.
Either of these solutions describe the approach of an agnostic. One refuses to accept either proposition the other accepts both. The former is done knowing that the lack of belief in one of the two is incorrect, and the latter knowing that the acceptance of one of the two is incorrect.
But whether you reject the truth or falsity does not matter. They both describe the same.