Is it illegal to park a private car at a bus stop?

Yes.

In China, it is illegal to park a private car at a bus stop. According to the relevant provisions of the "Implementation Regulations of the Road Traffic Safety Law of the People's Republic of China", in front of the bus station, first aid station, gas station, fire hydrant or fire brigade (station) and within 30 meters from the above locations Road sections are designated as no-parking areas.