Reading through that issue MDN was almost definitely in the right. Also calling them a long time contributor might be a bit off, from what I can see they did one typofix and added one link: https://github.com/mdn/content/commits?author=WebReflection
Wow, and the added link was another polyfill they had written, precisely the behavior that they were (justifiably) being questioned for in the original linked thread.
In the Medium article he actually references his only PR-- a typo fix PR-- as a recent MDN contribution and to open source. Some people just have an inflated sense of their contributions.
Reading through that issue MDN was almost definitely in the right. Also calling them a long time contributor might be a bit off, from what I can see they did one typofix and added one link: https://github.com/mdn/content/commits?author=WebReflection