Feedback FB11885183 filed earlier today.
macOS devices enrolled in MDM that are on 12.6.x and have the MDM Software Update deferral for both Major and Minor OS updates deployed will update to 13.1, with no user interaction.
This does not happen to all devices, so does appear a bit random.
On devices that have this issue we see this in the install logs. Devices behaving correctly - the 13.1 update is hidden from users and the devices do not automatically update to 13.1 do not have these errors in the logs.
Here are the logs when we see 13.1 install when it should not: