It's 100% the headphones. Much as you like staff to focus their complete attention on you when you are in an establishment, staff do not particularly enjoy feeling like someone's afterthought during an exchange. We're all trying to meet each other halfway in this world, but that involves making at least half an effort on each end. That staffer has likely had enough headphone/airpod/bluetooth "I'm sorry, what?" conversations with potential customers to see the worst-case scenario play out enough times. Consider their discomfort as well as your own.