There are two types of fuel cutoffs I've seen - an inline switch that cuts electrical power to the fuel pump, and a shutoff valve that's in the fuel line itself.
I have the latter, and it requires me physically opening/closing the valve to work. I've never heard of an automatic cutoff valve.
By chance, did your fuel level drop below 1/4 tank?
Built-in generators that get their fuel from the main fuel tank receive the fuel from a point that is physically higher in the tank. That way, leaving the generator won't unintentionally run your fuel tank dry.
Some new RV owners don't know about that and understandably get freaked out when the generator just suddenly stops working, but starts working again after refueling....