When I was about seven, my dad was the village bobby in Westfield, East Sussex. The police station was a small flat-roofed extension on the side of the house in which we made our home. What made this house interesting was the garden which was well over 100 feet long. A huge space which my dad pretty much turned into a small holding. Along with the huge amount of fruit and veg my parents kept chickens and geese. I can remember seeing eggs of all colours, shapes and sizes. Only the goose eggs were as large as the egg which is the subject of the linked story. We never ever had an egg within an egg.
I can only say that, finding an egg within an egg which in total weighed nearly half a pound, this is EGGSTRAORDINARY.