Isn't "dumpling" a food? She's comparing the ugly duckling with food?
Native speaker’s answer
Rebecca
She does not say "he is a dumpling", she says "he is a duckling." She is saying that since he can swim very well he is not a turkey and therefore must be a duckling like her other babies. I think there is a slight drop in the sound which may make it sound like she says "dumpling" a little but, but she definitely says "duckling."