Meta still maintained it and actively pushed commits to it fixing bugs and adding improvements. From this blog post it sounds like they are increasing investment into it along with resurrecting the original repo. When the repo was archived Meta said that development on jemalloc would be focused towards Meta's own goals and needs as opposed to the larger ecosystem.
This looks a lot as if the facebook/jemalloc repo inserted a single commit 70 commits ago and then rebased the changes in the original repo on top. Because the commit SHAs for the changes pulled in change you see this result.