Ah, my guess would be either they gave you a "wrong" egg or there was something else mixed in with that one chick. For sure I'd band it and keep track of it. Even if it grows to look like a campine, I'm not sure I would treat it as pure.
It looks a little bit like a Chamois Campine chick I've seen before. Chamois Campines are apparently 'made' by crossing a white Leghorn male to a Golden Campine chick, for at least 4 generations.
There is a lady in Louisa, Virginia who knows more about them, this is her site Cygnet Hollow Farm.
I've read it the opposite way, GC roo covering WL hens (I have a pen of them set up now). Take any daughters back to their father.
So far I only hatched out two a couple of months ago and I lost those two chicks. I hadn't gotten around to trying to set any more until recently I've collected a few eggs. I hate to raise too many chicks in the middle of winter. I also have a couple of two week trips coming up and my house sitter (my son) gets overwhelmed if I have too many separate pens to care for.
It's bad enough that I leave him with MANY hundreds of birds, alpaca, sheep, dogs, finches and the llama.
took a few pictures of one of my three silver campine chicks (hatched from Deb's eggs) this morning -- all three are looking like boys, and are a day past 6 weeks old: