Leaving the oil filler cap loose could have led to it falling out. Runing the engine with the oil filler cap off can lead to oil spraying all over the place. Fill it with oil and replace the filler cap. When was the last time the PVC valve was replaced? Replacing it might be a good idea. They are cheap.
Is there oil on the air filter or in the air filter housing? That is a sign of blow-by.