Here are the general bootstrapping rules of FPC:
- Latest release can be bootstrapped by previous release or itself
- Current trunk can be bootstrapped by latest release
3.0.0 can be bootstrapped by 2.6.4 or itself. Current trunk is 3.1.1, which can be bootstrapped by 3.0.0. But there was a time quite long ago, when 3.0.0 is not yet released, where 3.1.1 can be bootstrapped by 2.6.4 (the latest release at that time). 3.0.0 was released on Nov 2015, the article is written on Apr 2015. Now you see where your problem is: the article needs an update.
The solution is simply to grab 3.0.0 and use that as starting compiler instead of 2.6.4.