Has anyone ever been told they have a fatty liver?

I recently had an abdominal ultrasound and was told my liver appeared mildy fatty. The conclusion was “suspected mild fatty infiltration of liver”. When the doctor called to inform me, he said this is usually seen in older, obese heavy drinkers. I am 31, not overweight and never drink (never have). The doctor was confused and basically accused me of not being truthful with drinking and said to adapt healthier habits. I eat healthy, I work out 6 days a week so I’m not sure what I need to change now! I had an abdominal ultrasound a year ago and my liver was perfectly normal. Now I suddenly have a fatty liver without any explanation. My grandmother has had an enlarged liver her whole life and was recently told it was fatty so I’m not sure if genetics can play a role? Mine is not enlarged, just fatty but is it possible that there is something else going on or can they be certain it is fat on the liver? Now my mind is wandering wondering if it could be something more serious. Maybe I am thinking too far into things but the doctor really had no insight or advice for me so I don’t know what to think. I’m wondering if anyone else experienced the same thing and if you have any advice?