There are so many problems here I don't know where to begin but I'll try.
An "outlet" to connect a generator should actually be an inlet, that is, male connection. Otherwise you need a cord with 2 male ends to connect your generator and these are dangerous.
A generator connection should have an interlock or transfer switch to prevent the generator connection from ever being connected to grid voltage. Without this grid voltage could fry your generator and/or your generator could power the lines on the otherside of your transformer with thousands of volts and kill an unsuspecting lineman.
No generator connection should ever involve a 30 amp RV outlet. Your RV plug shouldn't have fit into this connection in the first place. Even though he used a female he should have used something with 4 prongs, the best choice would have been a twist-lock configuration.
IF, and that's a big IF, your RV uses a 50 amp service then you WOULD measure 240v between the hot legs. Why stuff blew up? Well, perhaps your idiot electrician also mis-wired the outlet and put the hot on the neutral or ground.
Either way, I would say anything in the RV is now likely damaged.