I'm not one of those people and my non-technical explanation is not medical fact, just an attempt to explain how ultrasound
is used for diagnosing cysts
. It cannot diagnose cancer or benign, but some features traditionally indicate a higher likelihood for one or the other, and that controls how the doctors will respond with treatment. If they think it is OK to wait a few weeks and re-check then, they are not overly worried.
Of course, doctors are humans, too, and can make mistakes.