SJ, these (and similar) types of aircraft are frequently used for overnight mail express courier work. Seats on these types are 'relatively' easy and quick to remove and replace to allow for light/small cargo operations. Sometimes seats are retained and mail bags fixed to seats and strapped in so they can't move. It'll vary dependant on the aircraft/contract/time/packages.
So, it is plausible that an aircraft like this would be configured for cargo operations overnight, and reconfigured for passenger transport during the day within an hour or two. The passenger cabin in effect becomes the cargo hold, some aircraft will also have a belly pack to allow extra cargo/luggage to be carried, though that varies from type to type. From images, this aircraft
appears to have been 'standard' configuration in simple terms, with no additional cargo capability, though I stand to be corrected.
http://www.iomtoday.co.im/webimage/i.../310864615.jpg
On this image you can see the 'cargo' door open at the rear of the aircraft.