Carma.... How do you tell if it's rug burn or if he fell on the ice?

My mans knee clearly looks like it has rug burn on it. No bruising, just red raw skin gone. matches pics on the internet of bug burn. He says he fell on the ice with sweatpants on. I cheated on my ex and got rug burn and said the same thing.. that I fell on the ice. Do you know how I can tell the differance? Can he fall on the ice and sc all the skin off his knee without bruising thru his pants?