There are two pieces of information -
i) the Doppler shift, revealing the instantaneous speed along the line between the satellite and aircraft during the "ping". Various three-dimensional velocities are consistent with this line-of-sight speed.
ii) the round-trip timing of the "ping", giving the distance between the aircraft and satellite during the "ping". A whole arc of positions on the Earth's surface are consistent with this distance.
If the aircraft turned around, then the rate of change in the timing distance would have reversed, and so would the sign of the Doppler signal, becoming higher in frequency instead of lower as compared with the broadcast frequency from the aircraft.
That the Doppler shift didn't change sign all the way to 0811, based on the Straits Times' excel figure, means that the aircraft probably crashed still heading away from the satellite.
However, after 0811 it could have turned, as there was no subsequent satellite data to check that.