I bet your non-RV electrician thought he was wiring up an old style electric dryer plug which when correctly wired is a 240 volt plug. I always DVM a "new to me" 30 amp source before plugging in.
We once pulled into a campground partially converted from being a mobile home park and a guest was bellyaching to the desk person about his shore power not being right and he also mentioned that he was a certified retired electrician. I was so glad I heard that conversation because someone had totally miswired our converted mobile home service pedestal and I could have fried my eggs well before breakfast if I had plugged in without looking closer. I was lucky.
