That’s why the dwarfs where helping him with his decision.

I think “train autism” means train spotting (the hobby, not the movie). In the hobby, you observe trains and write down their model and/or serial number in a notebook. The goal is to get a full set of trains of a certain kind, or operated by a company. Nowadays the community also posts photos on the internet, but for a long time, they were known as the guys comparing their notebooks with nothing but numbers.