I’ve always interpreted it as which came first, the chicken or the chicken egg?

I agree. And this boils down to how you define ‘chicken egg’. If the definition is “egg laid by a chicken”, then the chicken had to have come first. If it’s “egg that hatches a chick” (which will grow into a chicken), then the egg must have come first. But this ignores the pretty huge problem of picking a precise point on the evolutionary timeline where a non-chicken gave birth to a chicken. There isn’t going to be such a clearly-defined point.