Cable TV connections usually only have a very small amount of voltage/current carried in the cable. Unless you are familiar with electrical issues, I would let an electrician look at the wiring inside of your cable box connection. It appears that for some reason, more current was trying to pass through the cable than would normally be present. This could have come from a short in either the 12 volt or 120 volt systems in your coach.
Something caused a short in the cable and that short caused so much current to run through the cable that it melted it. The problem needs to be found and corrected before it does more damage.