I had the opposite problem, with parochial school teachers well versed in shifting back and forth between "it was a metaphor" when evidence contradicted it, to biblical literalism when there wasn't clear contrary evidence. So it was right when right, and meant to show us what is right when it was false.
I thought C&E was a philosophical question, like the ship of Theseus, it can't have a reductive answer because it represents ideals rather than logic.
To be devil's advocate for your stance, the '... an egg that was a mutation from non-chicken parents' were themselves derived first from an egg, which could be said to be the origin of the chicken, but itself laid by antecedent.... So eventually it must go back to the first entity that laid the first egg, and whenceforth they, etc...hence a philosophical perspective.