Your grass should have stopped growing. The reason it hasn't is because it's been so warm and sunny.... in more normal years I put the mower away in April
I think that's a little simplistic really - typically grass will continue to grow above 6c. Light and temperature are not the only things involved in foliage growth either, any high school student will tell you this - Light;Temperature; Relative Humidity; CO2/Oxygen and and source of nutrients.
Yes it's been warm and sunny in the daytime, and definitely more humid, but what about the heavy dew we get when it's been nice and cool for the last 3 weeks?
I found an interesting image from NASA:
While it was used to show the extent of growth after the massive flood event for QLD and NSW, it clearly shows a positive-neutral anomoloy for much of VIC - certainly not any 'browning off'.