Sounds more like he forgot to wrap multiple mutually dependent queries in a transaction. It doesn't require advanced technology to make a mistake.

To me it sounded like a pretty stupid race condition. Anyway, at least they reacted better than MtGox.

Their supposed fix doesn't seem like it would address the problem anyway. They should use optimistic locking.

edit: optimistic

And also skipped on testing that basic business rules can't be trivially violated.