In all honestly, despite Xu Anqiao's assumption that he was a knowledgeable person, he had never heard of a beast called the Yin River big carp.
The same could be said for many other beast appraisers.
When learning about various types of beasts, most beast appraisers got their information from books or encyclopedias.
However, encyclopedias couldn't possibly include every species that ever existed in the world as the author wasn't omniscient nor omnipotent. Perhaps only a small fragment of extant beasts was ever recorded in the pages.
And Xu Anqiao was aware of this.
Hence, he had a bad feeling that things might go awry today.
They only came to challenge Maple City's branch because the latter used private connections to apply for additional official positions, endangering their benefits in turn. But they never expected the situation to develop in such an unfavorable direction.