Hi,
Sometimes some atypical findings on the mammogram like the one you mention prompt further investigation to be certain not to miss a malignant lesion. In this case a repeat mammogram or a USG would help clarify what lesion was seen on the mammogram and you could discuss with your radiologist and physician what they are suspecting.
Receiving a callback is frequent about 5-10% of women receive them. If you perform the prescribed annual, the chances of getting a callback can go as high as 50%. This is all due to limitations of the mammogram. Though it is important to emphasize as well, how it has improved survival for patients, so we'll have to work with it.