RhIG has been shown to contain many antibodies. Since the product is anti-D immune globulin, how does this happen?

The processes by which immune globulin blood products are extracted from human plasma (RhIG, IVIG, hepatitis B immune globulin, etc.) involve extracting IgG, regardless of specificity. Thus, these products contain a variety of antibodies, depending on the IgG antibodies present in the source donors.