The average response time of the summary section does not always match the average response time of the details section once you dive deeper.
In the summary page, the total response time is calculated such that a test's response time will be set to 0 if 1 page failed.
In the detail page, the response time is calculated differently. A test's response time will set to 0 only if there are no successful pages throughout the test transaction. That is why you may see a different total response time for the two pages.