KenV - on this side of the pond we have a habit of understating things slightly more than you might be used to.
By "lower than intended" I should imagine BEagle meant "lower than ground level".
When descending by parachute, it's desirable to arrive at ground level with a sufficiently low vertical velocity to be able to absorb the impact with one's legs. In this case, the parachutists in question arrived at ground level "with a higher vertical velocity than planned."
Does that help?