Is this a Reason or Instinct Ability?
In my copy, it's listed as an Instinct Ability in the Ability section, but the example goblin character has "Discern Truth (R)".
Instinct makes more sense to me. Not the end of the world either way, and definitely rules-legal under the precept of custom abilities.
Good catch! I'd add a note to the goblin write up to point that out.