Yes over 30 years of dealing with chickens I have had my fair share of unexpected results and I have been left baffled and confused, but most of those birds were just run of the mill backyard birds, 20 years ago I started to get very serious about the science behind chicken genetics. For me it became rather easily. I can visualize over 100 genetic combinations on my head. Yet I have difficulties having a normal conversation with my Son or even my wife. For some people genetics it's more difficult to grasp.
The bird appears to be Silver Columbain in looks, yes the chances of an spontaneous mutation appearing right in front of your eyes is very real(it has happened before for other genes), but it's less than 0.1%, There is a 99.99% chance that what you have is a Brahma cross cockerel. He is quite handsome. Enjoy it.