When Nintendo updates the Switch’s firmware, the version number changes and at least a few changes are listed in the patch notes. To finish these updates, the console needs to restart itself. But once in a while, the company will put out a firmware update that doesn’t require a reboot.
Most “rebootless” updates are small and don’t come with patch notes. In fact, when Nintendo puts out new games, the version number doesn’t even change. Still, they are definitely a thing. Nintendo, for example, put one out tonight.