Traits Versus Quirks Carrying the Analogy into Groups
With a major NPC, a Trait determines how the character sees the world, thinks, speaks, and acts. For a group, a Trait would be a core aspect of that group's identity.
For a major NPC, a Quirk is something smaller that adds further individuality to the character. The same definition would apply to a group.
So, being "war-like" would be a Trait for a race. So would being musical. On the other hand, if the race had an interesting handshake, I'd call that a Quirk. It doesn't determine how they see the world or think. It isn't part of their core identity.
With groups, however, sometimes the line is a little blurred between what's a Trait and what's a Quirk. To me, this blurring is not a problem. The techniques are here to facilitate brainstorming. They're in the service of the final product.