The standard speed Cahuella enjoyed moving at was usually between mach 5 or 24, which would usually make it quite literally impossible for most people to keep track of unless they were some form of robot, like the computers which could see quicker than the speed of light.
He would keep his bead, for he was also not human; the precision of speed and sheer quickness of the Eldar was described as wrong by even superhuman Space Marines, who Eldar could move several magnitudes quicker than.
There was something else special about Axyrus Cahuella, though, that made him much different than other Dark Eldar. He was a Pariah. The collar around his neck was struggling and straining to keep the force of his anti-psychic passive aura from seeping like a dark shroud over the area, but when he wanted to, he could turn it off. He was also always aware of the orbs, figuring them in his calculations, the giant flame also was in there somewhere; rocketing up to mach 24 to reach about 1000 feet in about a second and basically INCREASING his jump, he ceased fire on Arik as soon as he began to soar, and then let loose with just his burst cannon on the orbs; the barrage of plasma would probably hit at least one of them (even though it was grossly accurate and Cahuella was an incredible markseldar) and presumably make the other explode.
From this vantage point, he would also probably be able to fire down on Arik at will. Maybe coding his weapons up to fire at the speed of light would help him quite simply snipe the mildly entertaining opponent.
If he had even witnessed the supposed quick movements of Arik, he would indeed not be nautious. At all. Superficially, the Eldar appear very similar to humans, though they are generally taller, lithe of limb, and fit, with sharp features and pointed ears. Eldar reflexes and movement are generally far superior to that of humans, their senses are sharper and they are more perceptive. While visually similar at a distance, it has been suggested that the most striking topical difference between Humans and Eldar can be seen when the Eldar move, exhibiting an extremely graceful and intentional manner that is not exhibited in humans.
An Eldar body contains no fat and their muscle fibers are dense and springy to support their agility and grace, along with bones that are lighter than human bones (and without marrow). Eldar reproduction is speculated to be progressive, so that the gamete delivery would occur in stages, with the need to add more genetic material at regular intervals. An Eldar heart is known to beat twice as fast as a human's and the Eldar brain has an extreme density of cerebral matter with sorts of ganglia and the teeth are outgrowths of the skull, unlike human teeth which are separate from the skull fundamentally. An Eldar has extremely advanced reaction skills compared to a human, their movements and reactions are almost too fast for human eyes to follow. An Eldar mind is said to process problems, emotions, and feeling in split seconds, much faster than a normal human.
The Eldar are long-lived by human standards, and most will live hundreds or even thousands of years unless they are otherwise killed.
Or in other words, they were far superior to humans and probably daemons and/or angels.