I suspect they might have flown an FR24 receiver on board with a realtime internet link through onboard wifi. I've done that before. The data is not present in another ADS-B network which has very good coverage in this area. I'm fairly certain they would have gone through the effort to make sure that path is visible if it has been flown and not left that to chance! Could even be that they bought the data for FR24 through aireon or another satellite based provider.