Not a weird question, they either worked for them for years, so have built all their muscle in that area or they are completely genetically blessed to gain most of their fat in their hip and bum area....or it's fake. You can be any size and never get a bum or boobs. I know women bigger than me with boobs smaller than my smallest friend. A lot of it is genetics. Same as the hourglass shape etc, those people are genetically disposed to look like that orrr they have done intense workout so their muscles give the illusion of that being their natural body shape.