Illegal Working Hours

A friend of mine is often working at night in Dar es Salaam, doing research on Mosquito. One night, she was stopped by the police and asked what she was doing. She explained, however the Policeman responded that working hours in Tanzania would be from nine to five, and beyond that working would be illegal, and that he had to take her to the post. She managed to sort out the situation later after a lot of negotiation. However she could also have asked the policeman what he was doing at this time of the day, if not work?