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 spinning at the impact.
To determine if the aircraft was spinning, IMHO, you should look in which attitude was before impact, the BEA statement does not clarify that.
A spinning object when impacting ground is horizontal and has a velocity vector close to the vertical. Unless you know the horizontal vector before impact you cannot establish if was spinning or not.