Bf doesn’t want our daughter to have his last name

He just brought it up rn when I got home and said “idk if I want our daughter to have my last name anymore” and I asked why and he said it’s because his last name is too “common” (his last name is nguyen) we both have 1 kid from previous relationships. We have set her name already and now all of a sudden he doesn’t know?.... idk if he’s trying to spare his other child’s mother’s feelings or what. (She doesn’t know that he’s about to have another kid with me and he said she will go crazy if she finds out)

The excuse of the last name being too “common” sounds so idiotic to me. And I feel like there’s another reason. Am I over reacting?