On the application, your son had the option to check boxes for certain demographics that applied to him. Those are for scholarships that are based upon the UC application. For example, there could be an entity that is awarding scholarships to twins from Tulare County, studying anthropology at UCLA. If your son fit that classification, when he is accepted, he might receive notification that he received a scholarship.
The Alumni Association scholarship is different. It is not based on the UC application. They have their own application which is why students received the email asking them to apply.