It is dominant because the super aka homozygous looks exactly like a normal pinstripe aka heterozygous. remember your punnet squares?
Pin x Pin breeding
PP = homozygous or super pin
Pp = heterozygous or normal pin
pp = no trait aka normal
the "PP" and "Pp" look exactly the same, therefore it is dominant, so to answer your question yes the breeder is wrong or just mistyped it.
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