εἰ + aorist indicative is not necessarily counterfactual, though it is here. Consider “If he said that, he lied.”
κεν φαῖμεν vs. κεν(=ἄν) εφαμεν (aor.indic.) is “we’d say” vs. “we’d have said.”
For an overview of conditional sentences see http://discourse.textkit.com/t/conditionals-a-guide/14120/1