It could just be that the developer’s native language happens to be English, reads books, and he/she used a familiar word without thinking twice about it. Because this is, in fact, a fairly common word.
Even "disharmony" is far more common than "disharmonious."
"And a sea of pulchritudinous models would have served as a lesson on how not to choose words: the ugly pulchritude sounds like the opposite of what it means, and it is one of those words that no one ever uses unless they are trying to show off.” https://www.goodreads.com/work/quotes/40167209-the-sense-of-...
That said, as a french speaker I would have had no idea what this word means if I did not took Latin in high-school.