That's the original date on the file, but the comment being discussed (and much of the code in that function, it seems) was from 17 years ago. See the git-blame:
See the text of the comment: "12/12/91". The `git blame` is likely due to not having imported the previous history as commits when the original import to the git repo happened. I worked at a company that moved from VSS to TFS for a ~10 year code base. It took months for the consultants to get the import to preserve the history. Too bad this didn't happen in this repo.
edit: Found this [0]
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it.
Let it rip!
https://github.com/torvalds/linux/blame/f4bc5bbb5fef3cf421ba...