It's odd; my first guess was Opera 1.0 release date, but that's in April. When it comes to arbitrary dates to use as the commit date, I have no idea why that was chosen. Maybe it'd make sense to someone with the actual VCS history!
There are only a handful of actual commits on the repo: two from 1995, and the rest from 4 days ago. It would seem that someone had a tarball of the source and specifically choose to backdate the commit, for whatever reason.