Don't thank me, thank the person(s) who discovered this and, in all likelihood, they, whoever it was, probably burnt their fingers during their intrepid quest for a clean iron. I honestly don't know how people come up with (obscure) stuff like this, but it works and becomes an invaluable service to the public.
This is my take. Once upon a time somebody got a headache attempting to clean their iron. However, baking soda or, whatever other old-school method they applied, didn't do anything. They went for the medicine cabinet to deal with their headache and pulled out a Tylenol tablet. Then somehow the tablet found its way onto the stained sole plate and a miracle could be observed. Suddenly the underside of the iron was clean - hallelujah!