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.
Suggested correction: If you're using a poison it is always worth having an antidote nearby just in case something goes wrong.
Lao Che could still have the real antidote in his pocket and give a vial a fake antidote to Indy. Plus, if you're implying Lao Che would need the antidote should he accidentally be poisoned, it would also be a stupidity for him to give the antidote to Indy.
Lao Che's goal is not to kill Indy, it is to get the emperor's remains without having to give up the diamond. He even tries paying for the emperor outright with valuable coins. He brings the antidote in case he loses track of the poisoned glass and the wrong person is poisoned. He never intends to actually give the antidote to Indy, he's only using it as leverage so Indy will hand over the diamond without making a scene. Indy only gets the antidote after he kills Lao's henchman and the antidote is knocked off the table.
