Autism is by its very nature a sensory impairment. If too much sensory information coming it at once is overwhelming to you and can cause temporary shutdowns, then you're being impaired by it. If loud noises raise your stress level to the point that you become distracted and/or disoriented, you're being impaired by it. If rapid or multi-layered conversation becomes difficult for you to follow and you miss relevant information as a result, you're being impaired by it.
On the other hand, if by 'sensory impairment' they mean "are you blind or deaf?" then that's a different situation. Perhaps you should ask, or write a note in the margins explaining what your sensory impairment is.
I caught part of an episode of 'Everybody Hates Chris' last night, in which he was running for class president. A question was asked about what would be done to help the school's disabled students. The stock answer: "ramps." Well, there you go - ALL disabled people are in wheelchairs. Who knew? This is the kind of idiocy you can expect to be confronted with forever. People don't know, don't care and can't be bothered to remember anything unless you can distill it into a five word (or less) catchphrase.
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"Strange, inaccessible worlds exist at our very elbows"
- Howard Phillips Lovecraft