When you disconnect the negative battery terminal for 10 minutes or so, the ECU loses some of the memory it has stored as to driving habits, and some of the operating perameters. Basically the ECU goes back to it's "new" default learning state. Then when you drive the car the ECU is learning "fresh" info, including the airflow from the new intake.
The ECU would learn this anyway, but it might take over 200 miles or more of driving before it incorpoates all the info into the way it controls the engine. Most people reset the ECU after making a "performance" mod, so it starts learning right away.