I don't think what your describe (a college student on a temporary job) constitutes being a resident of DC. So, he does not need to file a DC return. DC is "reciprocal" with all other states. He does have to report that DC income on his Ohio return (if he even needs to file an OH return*). Ohio will not give him a credit for what DC withheld.
So, he will have to file a DC return, but only if he wants the w/h refunded.
*The Ohio filing requirement is effectively $10, 650 for dependents.
