I agree with bogieboy. There is a lot more than air moving around in your crankcase. It is actually pretty tight in there. So what little oil collects gets squished, flung and generally misted by the crank. Then it ends up being burned with the air charge. IIRC my old KE125 auto lube pumped oil straight into the crankcase. But even the BRP direct injected Etec outboards simply pressure lube the bearings then whatever little oil that collects gets misted and burned. So that Ossa injecting oil into the crankcase seems perfectly rational to me because my first bike did that almost forty years ago.
640E, MXC200, XT200