Simply put, they are wrong. I have never ever seen a tank with a kH above 2 and a pH of less than 7. It simply can't happen unless you are using CO2 to keep pH down.

Raising kH above 1 degree and your pH will be ~7.1. Raise your kH to 6-10 degrees, your pH will be pushing high 7's if not 8.

Using a buffering substrate, ADA soil , Tropica soil etc. will keep tank water @ 0 degrees kH and pH at around 6.5.