Not identical technically but confusing as there is also regional variation in English as to what they would be called. Different species of the same genus and family though. Potiron (winter squash) is more commonly used in cooking - «soupe de potiron» but rarely see «soupe de citrouille» - and is smaller and more elongated. Citrouille ('true pumpkin') is larger, rounder, - more like the 'halloween' pumpkin that even those of us who have no interest in Halloween will know! If in the kitchen, guess 'potiron', if in the garden, guess 'citrouille' and have a laugh with the cook or gardener about how you always get it wrong when they gently correct you.