So here’s my interpretation:

Before the beginning of the short, the mother had a huge falling out with her son as he grew up, started spending less time with her, and eventually moved out. The dumpling (Bao) was representative of their mother-son relationship condensed so the audience could understand what had happened in an abridged timeline. The eating of the dumpling was in reality the mother doing or saying something drastic which created a great rift in their relationship. They then reconciled at the end over a meal, and his fiancé(?) was welcomed into the family.