The investigation will not be quick. The aircraft will have sunk in deep water and will take some time to recover, if indeed that is practical.
Fortunately all survived so the investigation will have a detailed report from the crew rather than a single comment from a passenger which has so far featured in the press reports.
Well done that pilot for the successful ditching and the local fishermen for the rescue, the outcome could easily have been worse.
Speculation is futile.