Resolved Maruti Swift VDI Diesel Engine oil change quantity concern

Hi I just got an oil change from the Shell petrol station to my Maruti Swift VDI. The oil change was free as I bought the engine oil from them. But the guy who changed the engine oil did not use the full 3.5 liter oil and he just left around like 300 ml or 400 ml of the oil left in the bottle itself, then I asked him why he had left the engine oil, for which he told, if we fill the entire 3.5 then there might be a chance of oil engine oil leakage from the vehicle, so it is better to leave some in the bottle itself.
So I just want to know is it good or what he did was right or not? I just want to know, whether I should approach the service centre and put remaining oil back into my vehicle or not?