They know, but the person they originally responded to is making a faulty inference in the form of "pigs = mammals, mammals emerged at X date, pigs emerged at X date". They aren't properly recognizing that eggs are a distinct subset of unicellular organism (which I also think isn't actually true of fertilized eggs) and you can't infer from the set "unicellular organisms" having a trait that "eggs" has the same trait.
An egg is technically a single cell. So, eggs came first as those were the first forms of life.
Eggs are single cells, but all single cells are not eggs.
Due to evolution, unicellular became Multicellular.
They know, but the person they originally responded to is making a faulty inference in the form of "pigs = mammals, mammals emerged at X date, pigs emerged at X date". They aren't properly recognizing that eggs are a distinct subset of unicellular organism (which I also think isn't actually true of fertilized eggs) and you can't infer from the set "unicellular organisms" having a trait that "eggs" has the same trait.