Multi columns are a UI choice as per the sage nostr:npub1jlrs53pkdfjnts29kveljul2sm0actt6n8dxrrzqcersttvcuv3qdjynqn. Desktop real estate is needed to fully make use.
The exciting part of nostr is that each column can be an interoperable ‘feed’ that can be swapped in either single or multi column apps.