Technically it’s not really hypocritical because the author never claimed that a lack of light mode is an accessibility problem.
I think it’s also notable that websites being accessible isn’t really about being tied to a specific theme, it’s about being compatible with accessibility tooling and standards (screen readers as an example). There are plenty of CSS manipulation tools that can make a website look whatever way you want.
Then all that'd apply to sites not having a dark theme, undercutting the author's point because he could just use stylus to.make his own dark theme for sites.
I think it’s also notable that websites being accessible isn’t really about being tied to a specific theme, it’s about being compatible with accessibility tooling and standards (screen readers as an example). There are plenty of CSS manipulation tools that can make a website look whatever way you want.