OP's co-author here. The biggest difference is that internships are short and low-stakes, so if something goes off the rails it isn't too costly for the manage

OP's co-author here. The biggest difference is that internships are short and low-stakes, so if something goes off the rails it isn't too costly for the managee or manager. Also, at least in tech, hiring is hard enough that interns tend to get the benefit of the doubt on "performance issues" in my experience.