I wouldn't say the "typical" motorhome has a generator auto start, but many of the newer ones do. Having said that the ones that do have an auto start feature also have a control panel that allows the owner to program the generator not to start during "quiet hours".
In all cases that I'm aware of the generator will only self start if there is no shore power and the batteries go below a level set at the control panel, or the temperature inside the coach goes above a preset level and the air conditioner needs to run.
Many higher end motorhomes are also equipped with an Aqua Hot or other similar heating system. If it was a cold night you might have been hearing it start and run.