When I read that earlier comment, I don't see "semi-autistic semantics" being used as an insult. I think it's actually quite relevant given the context, and appropriate given the argument that was being made.
Defining characteristics of autism (that is, the medical condition) include a deficiency when it comes to social understanding, a tendency to have an extreme focus on minor details, and an inherent inability to grasp the "big picture".
The earlier comment describes how certain attempts to justify what happened in a particular situation end up exhibiting similar traits. These justifications do not correspond well at all with how society at large interprets the situation, and they have a very narrow focus that ignores the larger social aspects of the situation.
I could see it being insulting if the earlier comment labelled somebody as being autistic in an attempt to discredit them, but in this case it's describing certain traits that correlate quite well with the medical condition and how those who suffer from said condition often behave.
If a person who suffers from a poor ability to understand the society around them, and who also tends to be unrelentingly focused on minute details, can be diagnosed as having "autism", then I think a similar diagnosis is perfectly reasonable when applied to an argument or justification that exhibits the same traits. It's a perfectly legitimate way of describing such arguments/justifications that don't mesh well with the social reality.