My understanding of the difference between Airwork (Air Ambulance) and Charter....
If the AoC holder (in this case Pelair) was contracted by the client (the insurance provider) to provide an air-ambulance service, for which it subsequently hired an aeromedical crew (Careflight) to perform, then it will be air work.
If an aedromedical service provider (in this case Careflight) was contracted by the client to provide an aeromedical evacuation, to which end the aeromedical service provider chartered an aircraft and crew from an AoC holder (in this case from Pelair), then it is a charter.
Will have to wait to see the investigation and the operational documentation to see which case applied.
Does anyone know if the CVR and/or FDR have been recovered?