Many if not most students with a disability other than intellectual impairment have comparable cognitive capacity to that of their typical peers. Often the difference is in processing speed, whether from a vision or hearing issue or in how signals are sent and interpreted. It’s like a computer that needs to buffer before playing a video. It can handle the task but may need some time. (Note: at :31 in the video linked above, the young lady shown has a learning disability.)
Individuals with autism have social deficits. This manifests in an inability to pick up on social cues or situations. It’s like a person who is color blind. Everyone around him can see a number in one of those color blindness tests but not him. The classroom is a social setting filled with social cues. A student with autism can easily miss out on important information. Here’s a link to a social experiment showing the difference in focus of individuals with autism.