Aaron is the first person to being close to right. First of all, it does not say "based on a true story" IT SAYS "Inspired by a true story" Meaning, the writer was sitting in his house, saw something about Ed Gein on the news, and decided to write his own story about a killer.
Its just marketing. Plain and simple.
And you know how I know it isnt based on any Texas urban legend? Watch any interview with the producer, writer, or director, and they talk about how it was "inspired" by the ed gein events.
And the Ed Gein movie,....it sucked. You could see dead people breathing.