It doesn't matter if it should have been commented or not. The reality is it wasn't. If you get in the habit of explaining your changes in git messages, every line change will have documentation, or at least an owner so you can ask them about it.
If you do need to go git spelunking to figure out what's going on, you'd have to be insane to not add a comment afterwards.
Either way, "shoulda coulda woulda". If the code doesn't have a comment, it doesn't have a comment. These things happen, and you can't change the past. But with git, you can relive it.