Tangent: when I opened this, I thought, “hot diggity, that is one fine serif font!” Then I looked closer and realized it’s the same font I’m using on my blog: Valkyrie by Matthew Butterick [1]. Nice to see such lovely typography on the web!
No I am pretty sure they are in fact commenting on the actual blog: https://lambdaland.org/ And I agree, it is a bit difficult to read with that font and color scheme. One persons "lovely typography" is another's visual noise.
Well, the white-on-grey colourscheme is quite unfortunate as it does make the text a bit of a blurry mess, but the formatting is fine. That is to say, on desktop the font size is well chosen and the line length is reasonable (if maybe a bit short).
...Just to be sure though, you are aware that the link in his post isn't his website, right?
[1]: https://mbtype.com/fonts/valkyrie/