Hello Luminous, and welcome to the friendly Camera Labs forum!
To enjoy your stay here please have a look at the house-rules
As to your Q: I don't know the camera, but it seems like it s doing some kind of extra processing with low-light photos. On some cameras there is something called "dark-frame subtraction" which subtracts the noise-pattern of the non-exposed sensor from the shot that has just been made. So this might be the reason.
Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews
, My Pictures
, My Photography Blog