Yes this is how “axis-aligned bounding boxes” work. Box3 should actually be renamed to AABB3 and Box2 to AABB2. I’m not going to explain AABB since existing literature extensively discussed this topic. Just give google a try.
Anyway, you need a completely different type of bounding volume that allows rotation (e.g. an oriented bounding box or OBB). However, proper implementations are complex and often require the computation of a convex hull first.