Судя по всему, это был пентестер, а подстановка была запланированной проверкой:

On Wednesday, just hours before both JFrog and ReversingLabs posted blogs here and here, a penetration testing boutique named Code White took credit for the packages.

“Tnx for your excellent analysis,” the firm said in a tweet that addressed Snyk and cited its blog post from last month. “And don't worry, the ‘malicious actor’ is one of our interns 😎 who was tasked to research dependency confusion as part of our continuous attack simulations for clients. To clarify your questions: we're trying to mimic realistic threat actors for dedicated clients as part of our Security Intelligence Service and we brought our ‘own’ package manager that supports yarn and npm.”

Источник: https://arstechnica.com/information-technology/2022/05/backd.../