Yeah, it's even in the OP: "Users saying that it's a good idea / product after a demo doesn't mean that the product has PMF. Users desperately wanting to use the product and pay for it ie., retention / repetitive usage is PMF."

The bigger issue is clearly that the advice boils down to something more like "if you don't have buyers, you won't make sales", which is just common sense and I'm surprised we need to have a whole buzzword about it.