Look at the eyes notice the ring around it like you see in pheasants , look at the primaries on the wings etc etc.. Only chicken in the pen was the rooster and the egg was hatched by a Silver Leghorn who thinks her purpose in life is to sit on eggs ..
Here is an Olandsk -- Yellow Golden cross . Just a pup yet but looks a lot like his Olandsk dad. This happened because we have a spare young rooster and he was getting his butt kicked in all the other pens so we put him in with the goldens. Seems to be doing great