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Those two explanations are quite reasonable, and do occur. Another possibility, which may encompass the original explanations, includes subtle attentional weaknesses, which would be another reason he might have been less interested in the easier questions, and more engaged by the "harder" ones. The main quality LNS and DSS (his strongest WMI performances) have in common is that they both involve using some kind of rule in reproducing the memory content, rather than straight rote memory. That is, of course, a more interesting task than verbatim repetition (DSF), and even than the ones with small amounts of manipulation (DSB) or distractors (PS) involved.
What about him makes you suspect a second exceptionality? Are there IRL functional or performance concerns?
