You ALL seem to be missing the point. I realize that it was my fault for clicking "YES", but there is no reason that I shouldn't have been able to remove them instantly, which the portal would not let me.
Very likely because somebody purchased them immediately. The portal wouldn't let you because they were no longer yours to remove from the market.
There is no possible way that anyone could have purchased them in the amount of time between when I clicked "Sell" and then "Remove from Market". It was literally a split-second, and I continued to click "remove from market" for at least 2 minutes before it actually sold. So I don't think that is what happened.
GAW probably has a bot that looks for errors like this and then puts in a split-second buy. They profit while you lose. Then they can tell you to gfys if you complain about a mistake.