Yes, despite the name, the Arithmetic subtest is really just designed to see how well you can hold and manipulate information in memory. The actual math is quite easy for the most part. Whatever was on paper must have been a different test altogether, probably the WIAT or the WJ-Ach.
Giving details but not getting at the heart of the question is another common problem in Asperger's.
Note that if a timed subtest is finished extra-fast, they get bonus points for speed, even if there are errors. So there may have been quite a lot of errors.
In any case, one would hope that the tester will interpret the data thoughtfully for you.
