is autism coded characters a thing?

Yeah definitely a thing. I'm not familiar with the book you had mentioned, but I know from the show Bones, the main character Temperance Brennan, is very autism coded. It's never officially indicated, in the show, what her deal is when it comes to social interactions, but it's been hinted on officially by staff and writers that she is autistic to some degree. It's not a very accurate portrayal of high functioning autism, however it technically counts I guess?