rather a snarky reply but if most think it is oil in the exhaust then I'll just agree to disagree until someone can explain how a lot of oil gets there and for only a short period before returning to 'normal' running..
I suggested the float gear and the nitrogen as a possible explanation without analysing the video frame by frame - it is also possible it was neither that nor the oil in the exhaust.
Snarky or not, I'll try to explain.
There is always some pressure in the return oil to the tank, which is necessary to vent off from the reservoir to prevent pressure increase in the system which in turn would push the oil through the engine where it will be burned and empty your reservoir in a fairly short time (which a clogged breather line will do)
As you have air in the top part of the reservoir in normal conditions, only the vapours are being vented off. An abrupt uncontrolled manoeuvre like in the video (possible caused by a pull from the external load), the oil will end up in the top of the tank where the breather line is attached and the pressure in the return will push the oil out instead of the vapours.
As the manoeuvre is back to normal with positive G's, the oil stop being vented overboard and the smokes stops..... as I said earlier, it does not need to be a lot of oil to produce this amount of smoke.