Wyatt and Nolan actually arrived late at the concert. They were busy with the fashion show and it ended late.
However, once it ended, they drove crazily towards the stadium to watch the rest of the concert.
Knowing that she was going to perform again, they wanted to see that moment with their own eyes. Unfortunately, they heard through the livestream that she won't be performing.
When they were feeling down, their moods got uplifted when they heard that she would be performing the song from earlier.
They never knew that she was that good, especially singing the local language.
Although Wyatt was with Diamond when she recorded the album, seeing her performing without stage fright made him feel like the child he had raised had grown up.
He felt really proud.
So, imagine his happiness when he saw the whole stadium chanting her name after singing the encore and then seeing her walking towards him after she was done.