I sent this article to my brother and he also misread that paragraph. The games he collects data from are as he says, "a small fraction of the hands he plays" So as a pro I'd expect he's earning a lot more, but for the cases of this blog post and probably personal preference he doesn't show the real totals of all hands across all games.
At 600 hands per hour it would take that long to play them regardless of whether this is a small fraction of the total hands. The rate per hour would be wrong if these are hands where he won less than usual, but in that case he's making a profound (but common) data science mistake by drawing conclusions from a biased sample.
Nobody is playing for a living at those stakes, I guess he was still learning at that time. It would make his basic analysis easier to bear out though. At those stakes the bad players are loose and passive, and simply playing tight and aggressive is a winning strategy.
straightforward tight-aggressive is a slightly losing strategy at these stakes due to rake (mostly because the other 8 players at the table are also using it)
Also, at 25nl there are many who play for living, as $500 is a decent salary to them
