Okay, in that case...

> They should have used a new term, not taken an existing one.

False premise. They didn't take "an existing generic industry term" and "give it a new definition". They took an existing definition[1] and tried coming up with a catchy new turn of phrase that they hoped would be adopted in lieu of "free software", and they were wildly successful. So successful that people convince themselves that "open source" must have already been a thing when Christine Peterson suggested it at the meeting where they settled on using it.

1. https://en.wikipedia.org/wiki/Debian_Free_Software_Guideline...