The 25–35 age group is not "extremely low risk" for a serious COVID-19 infection. The risk is lower than older age groups, but it's also substantially increased due to their higher degree of direct patient interaction compared to Stanford's executives and remote employees who did receive the vaccine. Also due to residents' high degree of patient interaction, they are at high risk of spreading COVID-19 to other patients and healthcare workers.
Which sucks, but is 100% the most efficient way to prevent deaths. Giving the vaccines to older workers first is correct.