There’s a faq entry about how these stats are computed [0]. Basically using git blame, since aider is tightly integrated with git.
The faq links to the script that computes the stats. It’s not designed to be used on any repo, but you (or aider) could adapt it.
You’re not the first to ask for these stats about your own repo, so I may generalize it at some point.
[0] https://aider.chat/docs/faq.html#how-are-the-aider-wrote-xx-...