Author here. I wrote this article as a guestblogger for Acquia, which is the company behind Drupal. I don't work at Acquia.
The article obviously uses Drupal as an example, PHPBB and Wordpress as comparison because they are all in the off-the-shelf, customizable category of PHP applications.
Both Drupal and phpBB (contrast to Wordpress) have massively modernized their code bases in the last years and improved the quality of their code. Coming from their original level, this is obviously a huge undertaking and still far away from being "high quality code" as an absolute measure. However their efforts in this space are remarkable.
Given that they have so huge installed code-basis that they have to take backwards compatibility seriously (which is also something that contributes to quality of software), explaining why it takes so long to improve the quality of truly old legacy software.
Compare this with many companies that use PHP, that still don't know what automated testing and quality assurance is. The article tries to highlight how PHP open source software use tools for quality assurance, what tools exist and that you should use them in your PHP projects.