My stepdad is a great and nice guy, and I've suspected for a while that he might be autistic. He's very quiet and reserved, rarely shows strong emotion. Chuckles rather than laughter. He's also fixated on certain things and hobbies, and can talk/ramble about them for quite a long time. He likes puzzles and, what have been given to him, legos. Putting together and taking apart things.
Like I said, no hard evidence, but I could see it.
I hadn't heard of that, but it makes a lot of sense.