This page about common accessibility problems actually has an accessibility problem of its own; the text is too thin, as it applies a font-weight of 300. The increased size helps but doesn't fully compensate. It's not just the mentioned color contrast that matters.

(Notably, many OSX-based designers will apply this lighter font weight because OSX increases the stroke thickness of all fonts, on display. So you'll not see the problem if you're using a Mac and you'll probably only see it on a hi-dpi display.)