What if he claimed that he was a member of the Ieshi clan? No, that won't be plausible. He didn't know anything about them except that they could predict the future.
He also didn't know the extent of Raeshka's talent about the Ieshi clan. She said that it was a clan of humans not demis so it was impossible that a monster like Souta was a member of the Ieshi clan. Plus, he already told her before that his tribe died and he was the sole survivor of that goblin tribe.
Huff...
Souta took a deep breath as he tried to calm himself. He shouldn't rush it. He would eventually find the truth in the future as long as he continued to increase his strength. At least, he knew that Raeshka knew something about the Ieshi clan. If he gained the power to rival hers then he would ask it to her again in the future.