Seriously. The jargon there is just a fancy way of saying autism is a form of brain injury.
You get microglial activation anytime there's damage to the brain and spinal cord. They're the cleanup system--they cart away damaged cells, like if you have an SCI or a stroke. Autism just doesn't act like a brain injury.
The "ongoing inflammatory process" idea is bunk, too. If that were the case, you'd have autistics with a constant degenerative process, kind of like what you might see with Alzheimer's. But that's not what you see with autism at all. Autism causes atypical development from the beginning, and autistics overwhelmingly show improvement, not degeneration, as they grow and learn.
The idea of "autoimmune brain injury" might be relevant for Heller syndrome, with its dramatic regression after typical development (though I tend to think the mechanism is much more likely to be something like it is with Rett's). But for regular autism, with atypical development, with the tendency to lose access to skills only under stress/burnout, if at all... it's not a relevant idea.
I think this is just a bunch of parents thinking they can somehow turn their undesirably autistic children into the regular children they really want, and using jargon to justify it.