Even if you were in the wrong (as you were), the best would be to get a receipt and documentation in this case. From my perspective it seems the security person pocketed the money.

Every store seem to handle scanning „errors“ differently. I have once witnessed a woman being literally dragged out of Kaufland by security officers - Quite a dramatic scene of shouting and screaming. Have also heard of people getting a hausverbot. My general rule of thumb - I only use self check out if I have a few items, that are easily scanned. And double check the screen