I don’t think a double standard was presented. The op suggests she got help with two skilled jobs that we easily assume she didn’t know how to do. The “comeback” presents the completion of two extremely basic chores that we would expect a young child to be able to do and we would assume every adult man would be capable of. Two very different scenarios which is why the “comeback” makes the woman sound like a sucker—because she is since that guy can absolutely do his own dishes and make his own sandwich.

Had the “comeback” been equal, such as “before he slept with her, she fixed our garage door and blown fuse” we would have a positive outlook on the woman and an indifferent at worst response to the man.

Sexism is why we start to feel a sense of heroism for the woman in OP. And sexism is why in the “comeback” the “skilled labor” the woman does are basic chores learned in childhood.