Ukmum, my DS8, who has Asperger's, is more gifted in math than in language arts, but he is extremely verbal and comprehends what he reads far above grade level. I believe the people who advised you about the comprehension score were misinformed. It is true that Asperger's can affect comprehension of fiction, and of others' perspectives more generally, but in very bright kids it does not always affect reading comprehension.
What tests did they use? An IQ test will not tell you whether someone is on the autism spectrum. Our practitioners prefer the ADOS for distinguishing spectrum from non-spectrum. Conner's rating scale and the Vineland scale of adaptive behavior are also useful.
I would be very concerned about the writing issues; I wouldn't let the school say they're no big deal, because they are. Our DS had these too, and it took a few years of fairly intensive private therapy to remediate them enough that he can do these tasks adequately.
To me, from your description, your DS has enough flags for Asperger's that I'd advise pursuing this further.
Best wishes,
DeeDee
