You're right. I see that in the Demigod preview manuscript (p. 257 for others who have it). I'm going to try to convert wyrdhamster's Heist above:

Threat starts at 0. No security (nor the Dragon) is paying attention to the characters.
Size is the size of the museum. This usually is the (Scale of the museum - Scale of the Characters). Because the characters are Origin level, the Scale and Size are both 3.
Legend is the level of magic involved: because Ladon (a Nemesis-level Antagonist) owns this Hoard, we'll put the Legend rating at 3.

This means that when...