If all you had was the WISC and WIAT, then yes, comprehending social norms was likely the Comprehension subtest, which is part of the VCI. A lot of different factors can affect performance, including social perception/social reasoning, level of acculturation, and receptive language. The meaning of the low score would depend on additional data on those other areas. (Completely leaving aside the issue of insufficiently controlled ADHD, which can affect any test. Comprehension is also generally among the last subtests administered on the WISC, so sometimes kiddos just run out of steam. You note that his dose ran out before the end of the testing session, so this is among the subtests most likely to be affected.)

Also, pm'd you.

...pronounced like the long vowel and first letter of the alphabet...