Current drawing issue on power switching part

Powered up arduino mega using a digital voltage regulator, I got the current consumption details on the regulator display. Then I connected the USB to my laptop for programming. The current drawing from the voltage regulator has decreased to half of its initial value and other half started drawing form laptop.

How the switching is happening?

Kindly help to know the switching property that's happening between LM358 and FDN306p.

The Arduino will draw from the highest voltage - presumably the voltage from the USB is dropping a little when current us drawn from it and the load ends up being shared between that and your power supply .