I wouldn't say they "broke" him.
They raised him with a lot of love and care, yes he imprinted, probably before they knew it was a drake and before they knew he would behave this way. Plenty of people don't realise what imprinting does to an animal longterm
Sometimes it ends okay, sometimes it doesn't. I'm sure this is a lesson learned for OP, and they don't need such a harsh response.
Instead of giving them one, how about you explain *how* to "fix" him.
