Conducting such pen-tests, and then publishing the results openly, helps raise awareness about the need to assume-bad-faith in all OSS contributions. If some random grad student was able to successfully inject 4 vulnerabilities before finally getting caught, I shudder to think how many vulnerabilities were successfully injected, and hidden, by various nation-states. In order to better protect ourselves from cyberwarfare, we need to be far more vigilant in maintaining OSS.
Ideally, such research projects should gain prior approval from the project maintainers. But even though they didn't, this paper is still a net-positive contribution to society, by highlighting the need to take security more seriously when accepting OSS patches.