what that question is asking: did they file jointly and did they have no tax liability but are only filing jointly to facilitate getting back their taxes withheld. you won't know the answer to this question unless you ask him.
for example, if they file jointly so they can claim the American Opportunity Credit, then their only reason for filing jointly is not just to get a refund of taxes withheld so neither would be a dependent (source IRS PUB 501)
