The metal grinding noise after a engine oil change

I have a 2012 Verso-S automatic ( UK based) and six months ago when I took the car to get the engine oil changed it gave a huge metal grinding noise for 3-4 seconds upon starting the car ( at the garage). The noise disappeared afterwards. 

That was my 2nd oil change on this car and it never happened during the 1st chamge as I always stay near the car to observe how they do it.

When I asked the technician he said that was because the pump did not had enough oil and upon starting the engine pump start pumping the oil to the engine or something. 

Is this normal for Verso-S? The guy did put the correct amount of oil too including tightening up the sump plug before adding the new oil.

Any idea what could have done differently to avoid this metal grinding noise come again at the next oil change pls? 

My car is 84k now and I prefer to xhange the oil every 6 monthly amd one due soon soI would lile to receive your thoughts on this problem pls. TIA