Yes, I agree with you. The article actually discusses that. It says that sometimes, in some of the polls, Presidents will "improve" over time. GW Bush I think was their example.Wow! There was simply Too much in that article for me to take it all in... However, what I did see to my Amazement was that Ronald Regan was rated as Best President in several polls? What? How is that even possible? I have been out of the USA for many years now but - I was there during the Regan years, and there is No way that I can imagine even ranking him as a good President!
IMHO Reagan was terrible.* but now it seems a lot of people remember him fondly. they even named an airport after him. My only explanation is that we have had worse presidents since so people might actually look back at hime and say, "well he wasn't so bad."
* seems like both control and abortion rights got politicized on his watch. And his economic policies were awful.