They made a PR that was built on top of another PR. The authorship information was preserved in the git history, and there was no attempt at deception. They also supposedly collaborated with the author of the original PR (which was never denied by either of them). All of this is totally normal working practice.

Those allegations of "stealing" just stem from a GH user piling onto the drama from the breaking change by pointing out where the initials from the new file format come from (which wasn't called into question on the original PR).

They were also not banned for those stealing allegations. They, as well as the author from the reversal PR were banned, as the maintainer deemed the resulting "drama" from the breaking changes to be a distraction to the project goals. The maintainer accepted the PR, and the nature of the breaking changes was obviously stated, so that drama wasn't completely on jart.