Interesting question! The st and ct ligatures used in the article don't seem to be part of the precomposed Latin ligature set, and what is there strikes me as far less obnoxious [1,2]. I expect it's possible to hack something together with combining characters, but also that the visual result would be far too ugly for the tastes of anyone who was desiring ligatures in the first place.
U+FB06 (LATIN SMALL LIGATURE ST) does display the same as the obnoxious ligature in the article if you have the right font. I actually used that for the "st" in the word "still" in my comment above.
In the HN comment editor it is the same as in the article, with that stupid curve connecting the s and t.
In the rendered comment in Chrome, Firefox, and Safari on my Mac it is using for regular comment text some font where the s and t are joined much less obtrusively. In fact at first I thought HN was replacing the U+FB06 on output with separate s and t. E.g., these two look very similar for me: still still.
For rendered code blocks on Safari and Chrome it is using the font that has the curve. On Firefox it does not have the curves. Here is a code block example:
