I don't get why people are saying, "I scored low so I guess I'm not autistic." Just because you score high on some 5-minute test designed by some British psychologist doesn't mean you have a brain disease...
You're right it doesn't mean, and typically they believe Asperger's/High Functioning Autism isn't a brain disease but rather a disorder (impairment in some area of life to the point professional help is needed. Also this test doesn't say one has it or not but rather traits associated with it, the key is if it's actually impairing one's life/human interactions. However something quite important to consider, you know how in the Scientific Method they have a control and experimental group? Well they've done the same thing with this AQ test in scientific peer-review journals, gave a control group (regular population) and an experimental group (those who have actually been diagnosed) and compared their means and standard deviations.
The general population averaged 16.4 and the Asperger/High Functioning Autistic group averaged 35.8. The standard deviation (or loosely an average deviation) for the general population was 6.3, and for AS/HFA group 6.5. 80% of AS/HFA scored above 32, however only 2% of the general population scored above that. Some food for thought, although it doesn't prove, it may be good reason for looking into a diagnosis if you score very high AND if you think you have social/other impairments. The reason I brought this to physicsforums was because Science majors scored slightly higher than the general population but not high enough to be in the AS/HFA range. So having a scientific mind I wanted to test it for myself (and found that this forum was a lot higher than the general population, even if mostly not high enough).
Reference: Scientific journal article which can be reviewed by other scientists
S. Baron-Cohen, S. Wheelwright, R. Skinner, J. Martin and E. Clubley, (2001)
The Autism Spectrum Quotient (AQ) : Evidence from Asperger Syndrome/High Functioning Autism, Males and Females, Scientists and Mathematicians
Journal of Autism and Developmental Disorders 31:5-17
http://autismresearchcentre.com/tests/aq_test.asp for a link where you can get it in PDF format.
Other peer-review research articles from the Journal of Autism and Developmental Disorders and Brain Research can be viewed in PDF form that link also.