Wonder what officer friendly would have done if the response to his demand was "I don't want to answer any questions". "Am I being detained or am I free to go?"
Would he have admitted that it wasn't a consensual encounter, and they were in fact detained? What if they had told him they didn't want to leave the store, and if he removes them to another location, then they will assume they are under arrest?
When police ask questions that would be none of anyone's business if they weren't wearing a blue costume, it's very difficult not to tell them it's none of their business. So I generally default to "I won't be answering that question, officer. Am I free to go now?"