This wasn't as uncommon as you might think. Aircraft identification was a never ending training endeavor. I know some of the 8th AF pilots had playing cards with silhouettes of enemy and friendly AC. Despite that it was easy to mistake one plane for another in the heat of battle or bad weather. There are stories of 51s shooting down 51s from another FG. US ac shooting down Spits, Mossies, etc...and vice versa. One story I read, a pilot got separated from his group after and furball and saw a group of three 51s heading home. He decided to link up with them until he got closer and saw they were 109s.