He should only have to file PA if no NJ taxes were withheld. According to the state of NJ:
Pennsylvania residents who receive compensation from New Jersey sources are not subject to New Jersey income tax on those earnings.
If you are a Pennsylvania resident and your employer withheld New Jersey income tax from your wages, you must file a New Jersey nonresident return to obtain a refund.
For more information: http://www.state.nj.us/treasury/taxation/njit25.shtml
