They were wrong.
The Wyandotte breed is always supposed to have a rose comb, never a Walnut comb.
Gentically, it is impossible to breed two rose comb chickens and get a walnut comb, so walnut combs will never show up in purebred Wyandottes.
The Silver Laced Wyandotte hen in your photo has a rose comb.
Rose combs can be flat (like on many Wyandottes), or they can stick up and be bigger (Hamburgs have bigger ones, and Red Caps have extremely big ones.)
Yes, Walnut combs can also be flat. Rose vs. walnut usually looks a bit different, and I am quite confident your Wyandotte hens (the silver laced and the gold laced in that photo) have rose combs. I'm not sure yet about the chick.