Kurapika fooled Uvo in a way that he couldn't possibly realize, IMO. Considering what Uvogin saw so far, the best assumption is that Kurapika was a manipulator (he was always with his chains on and could make it able to restrain someone as strong as Uvo somehow, either by strengthening it or by making Uvo weaker). In addition, Kurapika showed affinity with enhancement in the battle, so it made it even more unbelievable that he could be a conjurer (IMO it would more likely to think that he was an emitter, with double affinity with enhancement and manipulation).
Even then, if Uvo started the fight with gyo, it might've prolonged the battle a little bit, but he would eventually be caught IMO. Uvo is a close range fighter and, despite having ways of attacking from a distance, he would need to get closer to seriously hurt Kurapika... that way, he wouldn't be able to use his gyo 100% of the time (btw, his fighting style involves taking huge risks with a ko punch as his main technique... his incredible strength and durability made him too overconfident). We don't even know if Kurapika was concealing his chain with in right from the start, so it could've gone the same way.