Service transmission fluid

I had a sedan 1.6 with 6AT transmission, last week when I change my transmission oil, I realise that my mechanic charge me 5 bottles of 1 liter ATF oil. I confronted him sayin during last transmission service, another mechanic only used 4 liters ATF oil, why now extra 1 liter ATF oil needed? He explained after he drain the gearbox oil, he had to put in 5 liters of ATF oil and let the car runs for about 10mins and he had to "release" some new ATF oil to make it ngam ngam at the required level. So based on the explanation he gave...is it legit? Or I am one of his potong kepala customer?

*My own car booklet written it needed 4 liters only when servicing ATF oil