BTC240-BTC600?! I can't even imagine how much that all cost! I'm not yet familiar with trading, so how did he lose it? He sold all his BTC in hopes of buying it again for a lower price? I've been looking through the price change, it seems that plunges usually don't last long, it would be really risky to try this approach
It doesn't matter how short they are
That dude most likely had buy orders already in place, so if the price dropped only for a few seconds with just one big-time, wall-crushing sell order (as it often happens), he would have booked enough profits to cover his shorts. But he obviously made a devastatingly typical mistake, i.e. he thought he knew it better. But market always fools such types (and most other types as well, just in case)