It's not immediately obvious how a RoD can be derived from satellite pings.
As I understand it, the doppler shifts on the final logon messages are consistent with a high rate of descent. However, given the satellite terminal probably just rebooted after the engines failed, it's also possible that it was just a fluke while the transmitter was powering up.
Either way, it's one of the reasons for believing the aircraft probably spiralled in close to the final transmission.