Do you think it's appropriate for a man in a relationship to accept gifts from his female boss?

My boyfriend works part time at a daycare while he's in school for Early Childhood Education. He's the assistant for the preschool class. All his coworkers are women besides the cook. His boss who is a woman and a single woman at that said she was getting everyone sonic and asked my boyfriend what he wanted and he got a slushy. I feel like he should have denied her offer. Before anyone says "Well she got everyone sonic" I don't think that matters. End of the day it's still another woman getting him something when he's in a relationship. He just rolled his eyes at me and told me to grow up when I expressed my feelings.