Coming from a day and age where the women's role in the house was exactly this, this wasn't very sexist. I'll bet she was goddamn thrilled about it too!
I mean, if she regularly did the washing, it is a blessing to her to have it made much easier.
So - not really sexist. What would be sexist is marketing this to people as "help your woman wash clothes easier"
This was in fact endearing and not sexist. It shows an obvious flaw in societies new "modernized" I.E. overgoddamned sensationalized, view of sexism as it relates to todays working woman.
What a horrible husband, inventing something to make his wife's life infinitely easier, god that poor woman he should have bought her a useless diamond that just sits there instead.