Largest wild Umbrella Mushroom in my Farm

This is the largest umbrella Mushroom found in my farm, about 125mm diameter. Most umbrella mushrooms are small, generally less than 50mm. Why this one grew into such huge size?

The tallest human on this Earth is Sultan Kosen of Turkey, 2.51m. Most of us are less than 2m height. If suddenly, a 4-5m human starts to appear, what would you  react? Were there really Giants existed in the past as depicted in many stories of the legends, even Bible? I believed there must be so as Nature would try to produce all forms, sizes, types,etc., and let the fittest survived.