Quite a few people have armchair-diagnosed Jamie as "on the spectrum". (You may recall Ellen and Max riffing on the that topic shortly after meeting him.)In much the same way that I don't give Max a specific mental disorder or specific medications to treat that disorder, I don't want to nail Jamie down with a specific level of autisticness. I have always written him as an authour-insert, I write him like myself.
I have never been formally diagnosed, but I have had a few people speculate that I was "on the spectrum". I guess that's a trendy model of human cognition these days, a theoretically non-insulting way of telling someone that they're a little weird. You're not retarded or broken, you're just special! Y'know, like Sherlock Holmes, or Sheldon, or Data!
A few people have also theorized that there's some hidden plot twist in Leftover Soup, and that Jamie is actually a demon, or an alien, or a time-traveller, or a robot. That's something I don't get tagged with, but it is a common enough perception of both fictional and nonfictional spectrumfolk. (Insert commentary about witch-burnings and such here.)
I write Jamie like myself - more specifically, I write him like a younger version of myself. It's not so much that he's autistic or idiot savant or robotic... he is simply insufficiently socialized. I didn't spend much time with my friends when I was a young'un. Most of my days were spent either nose-deep in novels or glued to the television. As a result, I developed a deep understanding of stories and how they work, and a less-deep understanding of face-to-face interaction with my fellow human beings. Jamie's basically the same thing, but with boardgames and food instead of literary tropes and pithy dialogue.
I've evened out in my old age. I have a close-knit circle of friends now, people I like and who like me. Hell, I'm even married. I am no longer an optimized, minmaxed character - starting in my early twenties, I began putting points into charisma and charisma-based skills. Leftover Soup is a story about many things, but one of its main themes is Jamie gradually opening up and connecting to people the way I did.