I'm not sure of the genetics for crests. My Cream Legbar olive egg mixes have had dominant crests, but I have seen crests drop out pretty fast. It is possible two impure birds could match recessive genes to create crested offspring.
However, skin color is a wrong, body shape is wrong, tail is wrong, feather style wrong.
These birds are products of mixes, with Silkie close enough back to allow black skin and crests.
Tails are wrong for both Silkie and Cochin, so there was something else involved too. Ditto for feathers.
Point of pure breeds is that they breed pure with no, or very few, surprises if line is controlled.
This owner has mixed birds not Silkies or Cochins.
LofMc