You're right.Perhaps I am just misinformed (good chance, since I'm new to this stuff). I was under the impression that you needed a special transceiver to get these switches to play nice with 2.5/5gb devices, otherwise it wouldn't work unless the both devices supported 10gb.
But that's my point. If this is the one you bought, it shouldn't have worked. Maybe what you bought is actually a different model number?