I would agree that there are games out there where the people playing in them are all relatively good, regardless of the stakes.
On the other hand, I would imagine some of their skill comes from the fact that they know each other very well and play based off the tendencies of the table. This can potentially give the misleading impression that they are good at poker when they are in fact good at that particular game.
Additionally, when people say that 1/2 games are easy they are not saying all the players are bad. What is being said is that the tables are pretty easy (meaning several of the players make poor choices). There are probably quite a few decent players at even the casino 1/2 games. Though, if they were really good they wouldn't be playing 1/2.
Lastly, reading poker books
doesn't make you good at poker.
EDIT- also, 1 winning session doesn't make someone a good poker player anymore than 1 losing session will make them bad. I wouldn't expect to keep up that winrate if you continue playing at the casino.