Sorry this is 18 or so years late lmao… but I would assume the sideways pussy would be referring to how petite asian women are. Them being smaller… Would make their vagina smaller. Think about a normal vagina…
It goes from vertically between the legs making it bigger than a vagina that would be side ways between the legs… Makes sense to me 
… Where it came from? I dont want to speculate… But sideways pussy… that just makes sense.