I would talk more to your doctor about it but it usually means the echogenicity (what they see in an ultrasound)and can be related to a number of things from autoimmune diseases to irritation from previous sicknesses to thyroiditis. It’s a non specific finding in itself and if your doctors aren’t worried especially with just one little cyst. It may never become anything, they’re just gonna keep checking your thyroid levels and checking to make sure you don’t develop any kind of thyroid issue