You can see that there are glass vials above the lock now that you can see the inside of the chest. It’s a fairly basic concept: fill these vials with alchemist fire and if the lock is tampered with improperly, the vials break and burn everything inside of the chest. Being made of iron will ensure the chest, even though it’ll get hot, won’t cause the ship to catch on fire. Disabling this will require thieves tools.

As for his knowledge of sea lions you can roll nature. He will at the very least know that yes, they tend to be reserved for nobility as specialized hunting or guard animals.