Not my blog, but the author’s experience reminded me of my own frustrations with Microsoft GitHub.
Legacy means outdated. Not [necessarily] unusable or unstable or insecure or needs to be updated. But feels old or outdated. Conforming to older standards or workflows.
Wikipedia matches my understanding:
In computing, a legacy system is an old method, technology, computer system, or application program, “of, relating to, or being a previous or outdated computer system”, yet still in use.
Then I think the author also had a different understanding of the term, because he’s complaining about new functionality breaking an old feature. Introducing new code is quite the opposite of legacy.