Updates, so far, have all been user agreed. Every time someone updates their Wii and bricks it is because they have selected to do so and ignored the warning screen that their Wii may become inoperable because of homebrew content.
The update screen doesn't tell us what parts of the Wii it will update.
In your case you will get just IOS updates of a NSMB disc as your system menu is higher than that on the NSMB disc. How many you get depends on your IOS revisions, compared with those on the NSMB disc update partition.