Not every smart person or genius is Autistic lmao. The very fact that Light was so fucking good at reading other people basically proves the exact opposite of that, that he had greater Social Intelligence than the average person. He easily manipulated countless people for years, people are naturally attracted to him because of his Charisma (this is part of his Narcissistic personality disorder), except he's smart to the point that he can continue to trick people into thinking he's a good person unlike the majority of Narcissists, and he's also a Sociopath (or at the very least the Death Note caused him to become one) which is obvious from the viewer's perspective.