I don't think you did a bad thing at all. That's what those cars are for - going faster than anyone thinks they can.
Put a stop work order on your mechanic. I agree with the others here, as more than likely you had a leak at a seal, especially if you have the felt type crank seals. Oil gets thrown around the inside of the bell housing, and when you park, it drains off the hot engine and makes the puddle.
As mentioned before, it isn't the oil that indicates a blown engine, it is a mechanical symptom, and it sounds like you don't have any negative ones.
Noises, compression, smoke, uneven running - those things lead to a repair, which even then may not indicate a rebuild.
Keep us all posted.