Great. So there are two people beat the S&P500 after taxes and trading expenses. That doesn't mean that you or I can have any luck doing the same.
The key point of the article is that the delta between short term capital gains tax and long term capital gains tax will take a SIGNIFICANT bite out of any gains you manage in a trading (inherently short term) strategy.
For example, you set up two accounts with $10,000. One in the S&P500 and one that you trade. He ignores trading costs and assumes they are $0. For someone with a marginal income tax rate of 25%, long term gains are taxed at 15%.
At the end of the year the S&P500 account is up $1,000. You pay 15% on the $1000 gain for a net gain of $850.
At the end of that year the trading account would need to be up by $1,133 to take the 25% tax hit and end up with the same $850 net gain.
But people just look at the $1,133 vs. $1000 and think, woohoo, I beat the S&P500! I'm so smart! In fact, you just broke even because uncle sam takes more from short term gains. This preferential taxation makes it much harder to beat the market with trading.
So not only do you need to MATCH the S&P500. You need to beat it significantly just to keep up. It gets even worse as your income goes up because the delta between short and long term gains rates goes up to 20% at the 35% marginal income tax bracket.