Bike Caught on Fire!

My friend is on Deployment right now and I am watching his 2011 Sportster for him. Before he left he dropped his bike and left me with the repair work. Today I took it out for a ride around the neighborhood to run the fluids through it. I started to smell something a little weird and looked down at the exhaust to see that it was on fire! I got back to my house ASAP, put out the fire and realized that somehow, oil was leaking on to the exhaust and at some point caught on fire and was slowly burning. It was easy to put out and clean up, the bike is fine but I have no idea where this leak is coming from. I emailed my friend and just let him know that I took his bike out and it caught on fire. No other details. That'll keep him thinking for a while. I am an @$$hole