The message is that there are plenty of people who can invest wisely.
For the record, I also made money after the dotcom crash and after 2008, having avoided buying anything during the boom and buying blue chip in 2001. As well, I sold all my investments in Sept 2008 and picked up more blue chip in March 2009. Selling all my investments in Sept 2008 was more luck than anything else, I sold because I thought October was going to be the 80th anniversary of the Big Crash in the 1920s, but I was off by one year, it was 1929 not 1928. Better lucky than good.
My point is, anyone who made money on the way up, which it sounds like the author did, didn't believe that the markets would crash. The author didn't even show flat returns, it was always net positive before, during and after 2 crashes. It just doesn't sound right to me.
1. Buy when people are desperately selling (Get in when people are getting out).
2. Sell when people are desperately buying (Get out when everyone is rushing to get in).
That has always made money for me.
Learn and understand how investing works so you can take advice with a grain of salt and research the recommendations yourself. You also have to have a strategy that works for you and fits your needs, risk tolerance, and bankroll.