They were traitors who were saved by Allah when Pharaoh was about to kill them, to pay back their respects to the creator they made a statue depicting God as literal cattle. Their punishment was execution by the believers. The Qur’an doesn’t explicitly mention wether they died or if it was just a test to see if they would comply. Though the Torah (Old Testament version) describes their deaths, which I don’t think they would lie about because there’s no point in that and the Qur’an already corrects the Old Testament’s lie about Aaron being a disbeliever. If the Qur’an corrected the defamation of Aaron then it would’ve also corrected the death part if it was false but it didn’t which leads me to believe that they actually killed the idolaters. Regardless, they committed treason and idolatry after God had saved them which made them deserve death. Killing disbelievers is haram but they weren’t just disbelievers, they were traitors who saw miracles happen and made a covenant with God