Terrible situation OP but unfortunately, he has no legal recourse. Airlines are not travel agents nor do they represent the state department. Visa requirements can be tricky and may or may not apply depending on the travellers nationality and the destination. For this reason, the airline can't keep a comprehensive list of all possible scenarios to ensure that each traveller has the appropriate documentation. Not to mention that, especially when travelling to China, it may take a month or more to get the appropriate visa from the Chinese embassy prior to the trip. In the past when travelling to China, I've often sent my passport off for the visa before I bought my plane ticket. This is no different than airline ensuring that a traveller doesn't have some variety of criminal status or disease history (some countries will not allow you in, or scrutizine your entry if you are HIV postive, for example)

As others have noted, the airline owes him nothing. They are simply a vehicle for providing transit from point A to point B. It is ultimately up to the traveller to ensure they meet all of the entry requirements for a country.

Hope a suitable solution may be found in the very limited time he has to make it to the wedding! Welcome to FT!