Sounds vaguely familiar, and indeed I had bokmarked a site which did this exactly (just more elaborate, IIRC was built as a complete tutorial). Site (https://news.ycombinator.com/item?id=7450528) is dead now unfortunately, would have been good to get inspiration from. https://learngitbranching.js.org is still alive though.
It's the same guy so that probably explains why it looks familiar. According to the commits in this repo the website you refer to was the same content, only slightly delayed compared to the github page.
https://github.com/onlywei/explain-git-with-d3/commit/93fe62...
