Why is it called the pull mechanism in the observer pattern?

I can not understand why this method is called a pull mechanism.

Push mechanism in observer

public void update(Observable obs, Object arg) {
    // just update status
}

Pull mechanism in observer

public void update(Observable obs, Object org) {
    if(obs instances AAA) {
        // update status
    }
}

I think that the method called pull mechanism is nothing more than a filter in the push mechanism. If I'm right, why are you using it like that?