The ghostly shimmer that was K'Tath stood still, but he, too, was faced with a dilemma; Luke was running straight for him. If he moved, he risked Luke seeing his shimmering form - only a slight chance, but still not one he wanted to take. On the other hand, if he stood still, Luke would plow right into him. And those trainers were an added threat - a Lucario as K'Tath, with tech salvaged from an otherworldly wreck on his wrists, would make a prime prize for one of those trainers - and K'Tath did not fancy being, as he thought of it, "enslaved."
For now, all K'Tath could hope for was that Luke altered course and ran past him, his sight brushing off K'Tath's shimmering form as just part of the surrounding foliage.