"Observations of the tail fin and on the parts from the passenger (galley, toilet door, crew rest module) showed that the airplane had likely struck the surface of the water in a straight line, with a high rate vertical acceleration".
"Les observations effectuées sur la dérive et sur les éléments de la cabine
passagers (office, porte de toilettes, module de repos PNC) font apparaître que l’avion a vraisemblablement heurté la surface de l’eau en ligne de vol, une forte accélération verticale"
To me, it means that the plane's trajectory was rectilinear both in the horizontal (en ligne de vol) and vertical planes, with a velocity vector close to the vertical. It would also imply that the plane was not banking or not spinning at the impact.
Jeff