What mistake does Cole admit to?

From the text:

“I never told himhe was worthless,”Cole argued.
“Smashing his head on a sidewalk is a funny way of telling Peter he’s valuable.”
“That was a mistake,”Cole pleaded.
Edwin picked up his rain coat and headed into the pouring rain.“Hell of a mistake,” he called back, pulling on his coat as he strode toward his boat.
Wearing only a T-shirt, Cole ran after Edwin.“I’ve said I’m sorry!” he shouted.