The article says he was committed by a court of law. That is grounds to forbid one from owning a firearm. The arrest and adjudication should have shown up on the fed background check. What's the purpose if the records aren't complete and maintained by the State of VA?
It could be the simple mistake of improperly rendering his Korean name in the court records.
Cho Seung-Hui instead of Seung-Hui Cho.