It may be popular on GitHub because people pass out stars like they pass out likes on Facebook. (…) It indicates that it interests them, but not that they’re using it in production.

I’d somewhat agree with this. I “like” and react to content on Facebook to indicate my support, or to share my feelings and to interact with others. On Github, I’ll sometimes “star” a repository to indicate my interest/support to others, but more often than not, I’m indicating my interest to future me, so I can return to it later.