We're given specific reasons for why Solas seems to think and speak differently from others. He tells the Inquisitor up front when he first joins the party that he spent most of his life exploring the Fade. Ask him about himself, and he'll tell you as early as Haven that he spent most of his life wandering the wilderness, avoiding civilization, looking for ruins to sleep, looking for places to dream, and spent most of his life exploring the Fade and conversing with Spirits. Of course he's going to speak and think a little differently from average people who spend most of their lives awake and interacting with other average people just like them in civilized society. And we still learn more about him over the game beyond that.
Besides, there's more to autism than just thinking and speaking a little differently from what the masses are used to, and Solas fits none of the criteria. Autism and Aspergers is not the one-all, be-all explanation for people speaking and thinking a little differently from everybody else (especially when there is a reason given), and I'm tired of people acting like it is.