Google is on the internet. I don't always believe everything I read on the internet. This forum is on the internet, by the way, and so am I. Just saying.....
Breeds have tendencies. If someone is not breeding to the SOP then that flock may not follow the tendencies as closely as other flocks. I generally take general discussions of breed with two grains of salt and a dash of pepper as far as looking for something absolute. I just don't think most people breeding, hatcheries or individuals, are really breeding for things like egg shell color or egg size or similar stuff. They have their own goals.
There are still breed tendencies. But the flock is made up of individuals. Each individual is different. Just because Orpington have a tendency to go broody doesn't mean each and every one will. Mine never did. If you have a large enough number of Orpington for averages to mean anything then you probably will get some broodies, especially of the breeder isn't trying to breed broodiness out of them. Leghorns have been bred to be efficient egg producers, large eggs and lots of them. They have small bodies that don't require a lot of nutrients to maintain compared to a larger bird, so they have a pretty efficient food to egg conversion rate. That does not mean that each and every leghorn will lay a lot of large eggs, some won't. Some Leghorns may even go broody if you have a large enough sample size though most won't.
I don't put a lot of faith in the size of the hen determines the size of the egg she lays. There are tendencies but there are a lot of exceptions. Leghorns are fairly small but tend to lay large eggs. Speckled Sussex are much larger but tend to lay more of a medium sized egg. For what little it is worth my hatchery SS followed the medium sized egg tendency.
Derpy Bird is an individual. Averages don't really mean anything because there is only one of her. It sounds like she might be a leghorn, if you post photos maybe someone can help you with that, if it is important to you.
How many eggs has she laid that are that size? Is it every egg she lays or just some? Have you opened them, are they double yolked or somehow weird? There are different reasons that any hen may occasionally lay a really huge egg. So if you have opened one, is there anything different inside them?
If she consistently lays these extra huge eggs and is not a duck, goose, or turkey, then there is a glitch with her internal egg making factory that produces these extra large eggs. It is not a breed thing, it is not normal but some individuals are just different.
