The article is wrong because it merely explains the problems an economy would face if bitcoin replaced fiat.

Bitcoin is not a replacement for fiat, it's a niche alternative.  

For example, loans are basically impossible with a deflationary currency like bitcoin. In an economy where bitcoin were the only currency, loans would have to be done via some other method, or bitcoins would have to be redesigned to be either non-deflationary or with only minor deflation.

As for deflationary depression spirals, I believe these were often caused by the Fed mismanaging the money supply. Now it's true there were issues in the 1800s before the Fed, but I believe other/newer mechanisms could be invoked during a recession/depression to stimulate the economy rather than expanding the money supply.