I guess this ones are called as chinese mandarin orange. I have seen them too. They are smaller in size. But don't know if they are genetically modified.
Fruits and vegetables vary from region to region. Recently I have been amazed by the varieties of onions(white,yellow,red) ,potatoes etc available in the market here. I initially thought those orange , yellow,red capsicums were modified. But they are quiet natural and the colour comes from different ripe stage.