Agreed. I thought it was weird on the ct ligature on something like the second sub heading and the next one had a st ligature. I stopped reading the article and was just scanning for st ligatures in the text itself (there are none) and then realised the main font was a less legible serif font and the headings that were bigger and shorter were sans serif which makes the ct and st ligatures stand out even more.

I didn't read any more of the article after that, and the primary reason was just this weird font choice.