It is the traveler's responsibility to determine what, if any, visas are required prior to embarking on their trip. If there is ambiguity you should never rely on any third party to inform you of visa requirements but rather get the information directly from the embassy of the countries involved. All airline tickets state in their conditions of carriage (effectively the contract between you and the airline) that the passenger must obtain all necessary visas and that boarding will be denied if proper documentation is not presented.

The Chinese transit-without-visa (TWOV) policies have several nuances and vary between ports of entry. My research indicates that Wuhan is not eligible for multi-stop 24-hour TWOV for US citizens. Therefore, the airline was correct to deny boarding.