I don't think so, Catelept ... aren't the gem prices blizz-controlled?
I hope you're joking lol.
Actually it's kind of true. When you post commodities, the UI will automatically set the price to whatever the current going rate it, but you can edit it if you like.
Whenever the AH is lagging hard then the UI will first set the price as the vendor price and then update it once the server responds with the current going rate. I wouldn't be surprised if someone accidentally posted the gems with the vendor price filled in before it updated to the current going rate.