As the 'top' commenter, I'd say you're both right. It was partly a joke, and also genuine surprise, perhaps poorly expressed.
To try to be precise: I was surprised at Sana's implicit assumption that she should be the one supporting them. Given Ayane's aggressiveness/taking-the-lead and feel of maturity, I would say that if we were to assume either one of them would be the supporter/breadwinner, and the other the 'housewife', why not Ayane as supporter?
There is of course no reason they need to have a breadwinner/housewife dynamic, but tell Sana that.
And yes, there's no reason the sexual top has to be the breadwinner when there is both a breadwinner and a top. But, joke. Which is now dead.