Signy is more likely to have had common history with Thren's adoptive father. He was warrior caste and ranked high in the Gauntlet before he abandoned everything for the surface.
Thren would love Signy's attitude and be constantly surprised by her.
He'd also be amazed that she's a dwarven mage and knows how rare that is. He'd annoy her with all of his questions. He certainly annoyed Po with them XD