Autism is a sensory processing disorder. The way their brain processes sensory information is abnormal, with some sensory stimuli being very amplified and some sensory stimuli being very muted. Imagine lights being way too bright and sounds being way too loud to the point it overwhelms your brain. In distant times these people lumped into the same vague category as other people with brain abnormalities that made them unable to function properly or to function at a notably lower level than most other adults in their civilization.

Aspergers is a mild form of autism where the sensory processing abnormalities are quite subtle and so the person can be perfectly high functioning, but if you pay attention you can notice how they tend to hyper focus on certain things and be oblivious to other seemingly obvious things at the same time.

The idea that autism/aspergers is about the way a person thinks is a relatively new concept. It's like the "experts" tried to shove a whole personality and cognitive style under the autism umbrella. For example being highly interested in the finer details and inner mechanisms of how something works doesn't mean you have a sensory processing disorder, it just means that particular angle of analysis interests you more than other angles, nothing more or less.