While much of what you described as the function of the oil system is correct, it does collect impurities and then deposit them in the oil filter's filtering media, you cannot deposit an extra quart of volume there without making the filter housing larger. Loss of a quart or so of oil means you really lost it.
If you in fact lost a quart or so of oil in 60km, it either fell out on the road in a mightly splat for some reason, or it went out the usual way, which is through the engine and out the exhaust pipe. Spillage, leakage or some other external route would normally leave a few streaks of evidence.
I very much doubt a low octane fuel could inspire sudden and excessive oil consumption. In 60km you barely used a gallon of new fuel, in addition to what was in the filter, pumps and supply lines. In general for other than the octane of the fuels, the chemical composition of the fuel, including additives and grade of cleanliness is the similar for all grades at a given station. In some brands there may be more or less of certain "detergents" added in each grade, but the cheaper stuff is not something with chemically incompatible compounds in it that will attack your engine. So there is really nothing other than knock which should be affected, and your car apparently has the knock sensor to avoid this condition.
I would keep a close watch on oil consumption for a while, and if it returns to what it was before (I am presuming the new oil usage rate is much higher than before) I might repeat the experiment to see if the results noted in your post are repeatable. Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)