If I had a cystectomy, it is possible that the scar tissue from this is referred to as an echogenic cyst now?

Echogenic cyst. Probably not. What is being referred to is the ultrasound property of reflecting sound waves within a cystic structure. What it means is that there is a fluid filled cystic structure within your ovary that is resonating with the sound wave sent out by the ultrasound transducer.