In fact, the article addresses your point directly: Canonical contributed 548 changes in the period studied in today's report and would have cracked the top 30

In fact, the article addresses your point directly: Canonical contributed 548 changes in the period studied in today's report and would have cracked the top 30 if the foundation hadn't included "none" and "unknown" in the rankings. The maker of Ubuntu has been criticized for years for not contributing more to the kernel (and recently clashed with Intel over patches submitted to the company's graphics driver), but Zemlin [Linux Foundation Executive Director] isn't upset. "I am not at all mad at them. I think they do good work," he said. "You just kind of choose what's important to your org and where you can add the most value to the project and how it intersects with your business. They choose to focus a lot of their time and energy at higher levels of the software stack."