My theory:
They're cyborg android doo-hickies. If you look at their gibs, their bones are implanted with veins of glowing blue energy called
IMPULSE.

It drastically enhances their physical abilities, which allows them to run on walls, jump quite high, leap through the air and off surfaces with the greatest of ease, and be the fleetest of all feet around. It's all wired to their nervous system and to arms, hands, feet, legs, and torso. It energizes their frames, it enhances their capabilities, but at the cost that it must recharge after use, and that it also takes a physical toll on them, which is why it recharges faster when not moving and even faster when crouched.
Therefore, because of these bioaugmentations, it would only make sense they have the frame resilience to withstand falls from several hundred meters.
... ... That, and if you pay just a tiny bit of attention, you can see that their decent isn't as fast as a normal humanoid. Why? Well, try looking at their feet. Impulse jets? Hello?
[EDIT] At least at first. Terminal velocity doesn't seem to exist in Red Eclipse, so eventually they'll be falling ridiculously fast, but you have to fall from a reeeeally high place. The fastest speed I've attained was around 4000 (when playing with the flight bug, haha)