Impressive! Yes, warmer weather will always boost the economy no matter what car - warm up is where you are getting 15-20mpg until it's up to temp. I don't know about Honda but on Toyota cars they have designed them so they warm up faster by recirculating the exhaust gasses to warm up the coolant which in turns warms up the engine quicker.
If Honda employ the same, then explains why the blue light goes out so quickly.