Do coiled power cords heat up and cause fires?

"""However, if you try to power your RV with a 50' coil of 16 gauge wire, you can melt it. """"


I was walking my dog a couple of years ago and passed by a trailer where they were using a 50 foot extension to their 30 amp cord and the full length of the 16/3 cord was on fire. Amazingly they still had power to their trailer when I knocked on their door to tell them. The 50 foot extension was not coiled .