Scientific American has a blog post covering recent understandings about autism. The author points out that
Studies have found that long-range connections between different brain regions are weaker in people with ASD. Complex behaviors such social interaction and language depend on the precise coordination of distant brain regions. Some studies have found that people with ASD have enhanced short-range neural connections, which might explain why ASD can be associated with exceptional skills in specific domains, such as visual memory.
This would also go a long way to explain why concept-formation is slower and more bottom-up. If concept-formation requires connections among widely-separated areas of the brain, a strongly connected brain would make them more quickly, while a less connected brain would take longer. Processing would also take longer. But note that the short-range connections are stronger, which suggests why it is that the slower-processing autistic brain is also often a specialized and highly intelligent brain.
The autistic brain is thus less global and more local, with information spreading more slowly through the brain. It’s like having a city the size of Los Angeles without highways through it, but only city streets. Yes, you can get through LA, but slowly.