When a Hub is shared by public shared link, people who open it without signing in to Box see thumbnails for the files and folders inside it - in the Files block, in grid and tile views - rather than generic file-type icons. This gives an external audience the same visual, browsable Hub that signed-in collaborators see.
Thumbnails respect the shared link's access scope, so nothing is shown for content the viewer is not entitled to see, and any file whose thumbnail is unavailable or still rendering falls back to its file-type icon. No admin configuration is required.