TV has also changed dramatically in the last decade. With Netflix, Amazon Video, Youtube, etc (not strictly TV I guess but similar) it's possible to waste days on end binge-watching entire seasons of TV shows, in many cases ad-free. That was never possible in the past.
I'm having trouble parsing where you are disagreeing. The linked article says the average over age groups is about five hours, plus additional screen time on devices, with average time spent going through a dip when we become young adults, then an increase as we age.
I used to be in the Nielsen TV surveys, for the manual data entry (IIRC they had a thing that attached to your TV but I wasn't in the automated survey portion). They had some tiny reward program with a dollar showing up in the mail every once in a while. I believe the average person is probably a little like me and too lazy to fill in every single thing they watch and self conscious sometimes, too, about self reporting too much. The manual diary was pretty laborious.
