No, it means just randomly determined. As if you take all the cards in your hand, assign a number to each one, and roll a dice to decide which one you lose. But there's no reason to actually do that, you can just shuffle your hand facedown at let someone choose a card.
Thranduil
Thran has it right. In real life, you rearrange (shuffle) the cards in your hand and your opponent randomly chooses one from the back. In GCCG, it's exactly the same: shuffle your hand and have the opponent click on your hand number. This reveals the card backs. They can then pick one to discard.
