Yes, he was outright lying to the PC about his motives. Essentially, he'd graduated top of his class and joined the Talons, but defected to investigate when new recruits started going missing up north and the rest of the talons wouldn't do anything about it.
The reason I know this is because I had to get Bubbles permission to write for Quin when I first adopted him, and he told me Quin's backstory.
What I've adjusted it to is that Quin was following in his dad's footsteps to become a Talon (which is no longer a secret spy order, but rather just a specialized branch of military). He's a very, very minor noble only is the sense that he has a family crest, a last name, and a small amount of land that he and his mom share, since becoming a Talon awards it for members and families (note that it was granted to his dad, not him).
I don't want to spill too much for spoiler reasons, but how he came to join the cult aligns much more with what he originally told the PC rather than any kind of secret spy work.