Great piece, Kai! I got into UX design after training in sociology and years as a journalist. In both of those fields, we learned the art of asking open-ended questions, as both warm ups and cool downs. In user testing (really usability testing), it's almost as if, now that "the test" is over, the user relaxes and becomes more talkative, especially if you ask them questions about their area of expertise. You're right, you can get a lot of insight outside the formal "test" part. I always conveyed those insight to the product owner.