I guess all designers at fly were replaced by ai because this article is using gray bold font for the whole text. I remember these guys had good blog some time ago
Looking at the css, there's a .text-gray-600 CSS style that would cause this, and it's overridden by some other style in order to achieve the actual desired appearance. Maybe the override style isn't loading - perhaps the GP has javascript disabled?
and I think the intended webfont is loaded because the font is clearly weird ish and non-standard and the text is invisible for good 2 seconds at first while it loads:)