I don't know what kind of machine calculator you use, but most of them are usually a scam. Like the bodyfat a home scale would give you might give you some
indication, but is most of the time innacurate.
This type of scale would use a process called bioimpedence, which is the mesure of an electrical current in an organism. The way the electrical current is travelling in your body is affected by the fat % (fat does not let current go as easily) and give you an estimation of your fat %, depending of your weight and your height. It gives a good indication with results are know to vary a lot.
So don't panic too much about that.
Plus, as you said, breast are basically made of fat, which can increase the % you get!