My sister's Silkie, plus the other two silkie roosters I have came from a Breeder of Show Quality Silkies.Even if the chick is pure for partridge, it also has other genes, causing the excessive buff coloring. Meaning that it would not match the standard’s definition of partridge, making it a mixed color.
Also, Buff Silkies are also of Partridge Base, instead of Wheaten, which also maybe the explanation for the coloration.