Can you expound a bit? How can you correlate directly NPS and using TDD? Maybe it is that, for example, the new management/mindset/etc. that moved the dev team

Can you expound a bit? How can you correlate directly NPS and using TDD? Maybe it is that, for example, the new management/mindset/etc. that moved the dev team to TDD also moved the customer support team to be more responsive, and that's what increased your NPS. TDD reducing critical bugs hitting prod or stuff like that, I can understand - but NPS seems a bit odd.