To piggyback off Wolfess, you have to remember now every Retail auction house is connected now, no matter the realm or faction - when it pertains to trade goods. So you’re not just competing with your realm mates, you’re competing with every other player who just searched for that cloth and found themselves a deal.
And videos are not really accepted as evidence. I’m not saying you yourself are guilty of this, but videos and screencaps can be falsified. Blizzard only uses their logs of what happened. Likely someone just swooped in a split second before you did.