It's used here as a specific term from Seeing like a State[1][2], which is one of those books that got popular with a specific set of online tech folks. "Legibitility" in that particular sense is a very useful concept with no other convenient word, so I'm not too surprised it caught on.

[1]: https://en.wikipedia.org/wiki/Seeing_Like_a_State

[2]: available free to read online: https://files.libcom.org/files/Seeing%20Like%20a%20State%20-...