Stupidity: Lao Che's intention was to kill Indy. He had no intention of giving him the antidote. So then why would he bring a real antidote? Why not just fill it with something else instead? From his perspective, bringing a real antidote was a waste of time, and also very stupid in case Indy managed to get it, which he did. In fact, Lao Che could've brought a fake antidote and given it to Indy. He probably wouldn't have noticed the difference, and then there wouldn't have been a fight in which one of his men was killed.