Rashi seems to be explaining what the Gemara means by "destroys the house;" he understands that it means this literally, referring to the physical destruction of the house (for had it meant that it will destroy the marriage, the Gemara would have said so). Destruction of the house means that the house will literally fall apart (or have to be sold). This seems clear from the Gemara logically, because if the Gemara was explaining that anger and promiscuity destroy the marriage, then why does it say that it applies only when the woman acts in these ways? Certainly when the husband acts in these ways, it will also destroy the harmony and trust in the home! Since it is referring only to the woman, it must be that the woman's misconduct causes a form of destruction which would not be caused by the husband's misconduct -- and that is why Rashi explains the way he does.

Moreover, the woman's promiscuity and anger does not necessarily affect the harmony and trust, because regarding her anger, the husband might assume that he can appease her at a later time. Regarding her Z'nus, she can hide her infidelity so that her husband does not know about it. Hence, Rashi realized that the Gemara was referring not to the harmony of the home, but to the stability of the house from a practical standpoint.