Ask HN: Tracking activity on GitHub – where commits come from

I know github (the site, not enterprise) does not support looking at the IP addresses of commits. However, there is a timestamp associated with each commit and a GMT offset. Is that GMT offset accurate to the timezone where a commit is generated? Or relative to the person doing the commit?

Are there other ways of finding out where commits originate?

The use case here is trying to figure out if a contractor is outsourcing the work to other / cheaper labor.