I like the idea that Kapura simply knows something we don't.
When he is practicing in Ta-Wahi, he says he can "feel" other places.
"If I practice, I can be where I am not. I think I can feel it. It is hot here where I am, but where I am not is cold, and I think I can feel it. I must practice more."
He later shows up in Ko-Koro, which is "cold". This makes it sound like more than just simple teleportation to me. I think that with the help of Vakama's previous research and long, tedious meditation and 'practicing', perhaps Kapura has learned how to compress spacetime around himself. Perhaps he used his natural energies to somehow manipulate and cause small wrinkles in spacetime so that Ko-Koro was closer, almost putting himself in two places at once. In travelling to Ko-Koro this way, he would still be moving as slowly as ever, yet to outside observers it would appear that he has sped towards his destination even faster than the eye can see. Matoran have innate elemental energies, so it seems feasible that after thousands of years, someone could have learned to manipulate their energies to develop unusual abilities.
Thinking about this more, it would seem that Takua, who was right next to Kapura while he was 'feeling' Ko-Koro, would have felt it if Kapura was compressing spacetime nearby. So perhaps rather than distort spacetime around himself, maybe Kapura is able to stretch himself across spacetime. He would still be moving impossibly quickly by moving very slowly, and only he would be aware of the distortion, leaving bystanders to watch him simply disappear.