The bag pipes are plastic
Anyhoo, oil in there is normal. Basically oil vapour from the crank case is drawn up through the breathers to a point just before the throttle body. (this is how the breather vacuum is formed). When the oil is hot, it is fumes, however as it cools, it condenses back to oil. When you switch off, the hot oil fumes from the crank case continue to rise into the breather bridge where they condense back to oil, draining down infront of the throttle body and down past front multiram to the bottom of the intake duct.
This builds up over time, but you would need there to be a couple of litres in there before the engine intake vacuum could hoover it up, and even then, once it can draw enough air from the air filter, then it would stop lifting the pool of oil.
It will draw some oil from the surface on a prolonged run with alot of throttle, but you're talking crosscountry autobahn speeds, not daily driving. Also this is getting into the realms of fluid dynamics, which is kind of overthinking it
Oil on the tray is more likely to come from the oil pressure switch of front crank seal than the air intake as I don't believe that there is a drain hole between the air filter and the throttle body (potential for debris to reach the intake).