AAA sometimes sends its members (including me) literature stating that they are eligible for discounts up to half off at Starwood hotels. I always assumed it was like the SPG50 certificates -- usually (but not always) a worthless discount off a highly inflated rack rate.
In the many times I've checked the AAA rate, I've never found it particularly compelling -- but it sometimes is a few dollars less than other discounts. Obviously, you found that rare example where the discount is substantial. Congrats!