It looks like a state actor, but hard to tell who. The way they did it was by bullying the original overworked maintainer into making someone else a co-maintainer, and that new co-maintainer introduced the backdoor. The accounts that pressured him into adding another maintainer all appear to have been sock puppets.

It just shows how little support there is for the lone maintainers of basic utilities that we all use, and it's really something we need to do something about.