Who knows and who cares? Maybe they happened to have an investigator right nearby when they heard about it? Maybe it's a new investigator doing something for training? Maybe they have a special interest in Vixxens because of all the prangs you mentioned? Maybe there is a link between the Pilot and other ongoing investigations?
Why even post this? "Oh no, the ATSB investigating an incident?! DOING EXACTLY WHAT THEY'RE MANDATED TO DO?! how scandalous, the people must be told"