Yup, despite there being today (in the town where the flick was made) plenty of people who will swear blind to having known the family, spent time with the perp in prison, yadda yadda
; the TCM story isn't true at all. As ariesrising said though it was probably inspired very loosely on some level by the real-life serial killer Ed Gein.
P.S. It wasn't a stupid question.