1. They didn't know it was doomed.
2. They zoomed out because they saw a second trail and wanted to get it in the picture.
3. From what I read, WFAA was setting up for a different shoot, and the camera guy took the opportunity to shoot the Shuttle, too. Sounds like he used his pro-quality camera.
You also have to remember that the shuttle lost contact with the ground BEFORE it was over Texas. There were some folks here on FR who reported from California that it was already starting to break up when it passed over them.