Today I went into a small local shop to buy a loaf of bread. The minute I walked in, the girl at the counter told me to close the door "properly". Not in a mean way, just very blatantly. There were three workers in the shop and me and one other customer. Then I asked a different worker, if there was any bread left, and he said that there wasn't so I said no problem and left. Why am I so upset by this so ordinary encounter? 

For context I'm quite a generally anxious person.