Jostens accidentally sent me diamonds instead of CZ?

So, I got my new class ring today (it is a "Sheer Ice - Heritage" ring) and as I opened the box I noticed a small piece of paper. It was a Certificate of Authenticity that said something along the lines of "Jostens guarantees the enclosed ring to contain genuine diamond(s)." Thing is, I ordered Cubic Zirconia instead of the diamond, as the diamond ring was about 800 dollars out of my price range. Did Jostens make a mistake and send me the wrong kind of ring? I mean, I'm definitely not complaining, but I'm just curious.