Why do mechanics switch engine on during oil change?

I previously did an oil change at a garage and I noticed they add the oil then switch the engine on let the oil go down and then add more oil befor switching it off and letting new oil come back

However surely this is the incorrrect way of doing it. When you switch the engine on the oil goes into the engine parts and when you switch it off it returns to the dipstick level after a few minutes where it should return to where it was before you switched the engine on.

In this case the oil was a bit over the dipstick level but they told me not to worry.

However am I correct in saying you fill it up with the engine off up to max and that’s it then you switch it on. In worst case I imagine only after switching it off for a few minutes can you check the level again as the oil has returned the you add if needed.

Like I say it was a bit over max which could have been avoided and I have noticed more than 1 garage do this. In one case my friends car oil was well over max.

So are these guys doing it wrong or is there some correctness/wisdom behind this?

Thanks

Are they doing