Sort-of correct. When you have bunch of instanced static meshes, bounding box of all of them is considered for view culling, and when it overlaps, all of them are sent to the video card.
If you have 4 instanced actors, each with 10k instances, and you’re looking at only one of them, only that one (and its 10k copies) are rendered. If your view includes all four, then all 40k instances are rendered.