Blood spot in eggs

I was eating hard-boiled eggs this morning, and came across a spot of blood in one. I was always told over the years that a blood spot in an egg means the egg was fertilized. Is that true? If so, how do they end up being fetilized in the sort of battery-farm environment most eggs are produced in these days?

Do you know where the chickens you got eggs from live and that they are kept in cages at all times?

They’re not the result of ferilization.