In India, the reason for the increased shipments is most likely Nokia increasing its smartphone shipments expecting an increase in demand with the launch of budget handsets such as the Lumia 620. Nokia's also trying to market its Lumia 920 and Lumia 820 handsets via television and print campaigns. So it won't come as a surprise if shipments are higher than that of the iPhone given that the iPhone commands a much higher retail price.
Also, similar to other developing markets where import duties are high, a lot of iPhone sales in India are unofficial and come from the grey market, which IDC doesn't count. So the shipments are not accurate indicators for actual sales.