There is some good information and also some misleading statements in there. While ORP is definitely related to sanitizing ability, it is not nearly as directly connected to sanitizing ability as that article makes it out to be. ORP is not the best measure to use for sanitizing ability, despite their statements to the contrary. Several factors can change the ORP reading without changing the sanitizing ability at all. For ORP to work those non-sanitizing factors have to be controlled and accounted for, normally by calibration to other test methods.
The article casually dismisses these other factors that can affect ORP readings as contamination. While in some technical sense true, there are things other than water and chlorine in the water and you can call them contaminates if you want to, in practice there will always be things in the water other than water and chlorine and you can not simply ignore their effects nor is it practical to remove them.