Well like most youths, he could just think it makes him look cool...That's it. Considering that he also is hanging out with the "cool group" that is team skull, I can see why he wants to make a cool persona for himself.
This is a good example. I'll never forget the incredible Owain from FE. However, Owain was extremely overt with his thinking he had special powers. The reason I originally asked about it is because I don't see this in Gladion from the information we have so far.THE Owain and his sword hand.
Youth can exhibit these traits, but they don't all (if they do, I haven't noticed many instances with my 400+ students in the past). In many cases of real youth exhibiting these beliefs of holding special powers, it is a minor symptom of possible mental illness, however the symptoms may not be recognized, severe enough, or coinciding enough to result in diagnosis. Youth are also quite imaginative and the two qualities can play off of each other, or be unrelated. This can be reflected in the level of dissociation happening with the student, including how it is manifesting and how it is influencing their ability to function, interact, etc. With the strange things happening in Alola and the fact Gladion has Type: Null, it is more likely he actually does have something going on with his hand twitching and it's not just delusions. Of course, he may fall into the chunni stereotype, but I would need to see more information before this is decided. I thought perhaps we already had that information, which is why I was confused his hand twitching is the only thing pointing in this direction.