(Autists perspective)

It's not new at all, the term has been around decades and itself has been around literally forever. It's a different brain development. There are many historical persons which are thought or know to have been autists (e. G. Einstein, Lewis Carroll, Dan Akroyd to just name a few over a longer timespan.)

It's also not having autism (as an optional trait) but rather being Autist (as a defining foundation).

Just like, say, mutations that also always happened to certain degrees.

Feel free to ask. Also, of course, that is my personal opinion where it is not scientifically proven.