The "Diagnostics" he is referring to is ECU codes, and if you didn't have any of those before the "ECU learning", you won't have any after.
If you had, say a bad oxygen sensor, it could cause the long term fuel trim to adjust. After that got fixed, then you could disconnect the battery and it would help because it takes so long for the long term fuel trim to adjust itself.
If the same oxygen sensor was going bad, you didn't fix it, and disconnected the battery, then it would run worse because there was no compensation from the trim.
The ECU is always adjusting itself because of input from the sensors. "Cleaning it" isn't something that you would need to do.
I had to dissconect battery becouse i had to remove injectors from the engine for cleaning. After i mounted them back, when i tried to start the engine, it did not started for some 4-5 seconds so i slightly pressed accelerator pedal and then it started (but also ecu memorised what i did). After that every time i tried to start engine i had to press accelerator to start and it started only after few seconds..
Today i tried same procedure as described on daewootech (for idle) forum and now it start almost momently without touching pedal.
After you replaced the injectors, it wouldn't start right away because you had to build up fuel pressure again. When you disconnect the fuel lines, all of the pressure that stays in the line escapes. Then the injectors starve for fuel.
Because the vehicle is fuel injected, pressing on the accelerator when in the process of starting doesn't do anything. The ECU gives the injectors what they need to make the engine start and overlook what the pedal does.
Disconnecing the battery would reset the ECU anyway, no matter what the Daewoo forum says. There's nothing in that post that would have helped you.