The letter is a form letter and they are never specific to any particular case. The additional views are Good Medical Practice ..... everything and anything that leaves even the slightest question should be checked until a definite conclusion is reached. Call backs are not at all unusual. Regards..
Sometimes there can be smudging from deodorants causing bad images. Sometimes there can be cysts or sometimes it's just a bad image. They said most findings are probably benign, because they are. Hormonal changes cause cysts to become common, not every woman gets breast cancer, and they don't want you to be afraid. But they want to be extra sure it's nothing. Also having a good, clear picture gives a better reference just in case something does change in the future. It's the same reason they ask women in their 20's to do self exams. You're unlikely to get breast cancer that young, but if there are any changes you're more likely to notice them.