I think it could make a pretty large difference, actually. Languages like JavaScript (I know it's not included here, but still), Ruby and Python have large open source communities creating time of libraries in common usage. Compare that with a language like C#, which has an extensive standard library and comparatively less open source third party libraries. You'd expect that even if there was an equivalent number of private repos in both cases, the languages with a larger open source ecosystem would appear more popular in this analysis.

My private repo usage is heavily C#