Pretty sure he meant "rooted" in the sense of "inserted exploits into the codebase". In some sense that's much worse that mere root access to the host. Such a database could, for example, phone home with all updates to tables named "passwords", etc...
And even in the more banal sense you interpreted, sure: you might not run mysql.com-sourced daemons as root. But you almost certainly run the mysql command line utility as root from time to time.
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Don't even the most basic MySQL install tutorials have you create a separate user and group for the database user?
If you're running MySQL as root, you're trying hard to get owned.
Pretty sure he meant "rooted" in the sense of "inserted exploits into the codebase". In some sense that's much worse that mere root access to the host. Such a database could, for example, phone home with all updates to tables named "passwords", etc...
And even in the more banal sense you interpreted, sure: you might not run mysql.com-sourced daemons as root. But you almost certainly run the mysql command line utility as root from time to time.