Seen more than afew just like him- silkie mixed with game. small crest, rose comb body type, short legs from silkie, clean legs and large tail from game. I've even made the cross myself to test out as setters for peafowl eggs.
It is very easy to lose the black skin and extra toe plus normal skin is not THAT rare in silkie, plus there is no reason he could not be a second generation onwards from even a real good and perfect silkie. 2nd gen mix or whatever could fit in for his splash color, however blue is more than common in both silkies and games so it still could be a product of pure game crossed with a silkie, especially a hatchery stock silkie.
As a test, you could breed him to his daughter or a silkie and if any of the chicks come up silked, there is your proof.