After delivering the first beta of macOS 13.2 yesterday, Apple is providing a quick security update for this same preview tonight. This is a first for macOS Ventura, while the manufacturer has tested (twice) the same mechanism on iOS, during the development cycle of iOS 16.2. It is also very possible that this is also a test.
Downloading this update is quite fast, more than for a beta anyway, but you have to restart the Mac. This system allows Apple to quickly distribute patches on iOS and macOS, without waiting for full versions of the operating systems. Normally, these updates are supposed to install without needing to restart the device, but this was the case for tests on iOS as well as for macOS (on the other hand, the restart is much faster).
macOS Ventura: How Apple rolls out fast, no-reboot security updates
An option to disable the installation of these updates is available in the System settings > Generalthen click on the small i to the right of the option Automatic updates.