Eh?

This is if you a) purchase the phone in some way that is associated with your Apple account, b) have cloud backups already in place, and c) opt in to the preload.

If any of those things aren’t in place, it wouldn’t have happened.

Now your likely assuming they can get into that backup, which fair enough would be a concern. But (if you believe them, which I admit is a huge if) according to Apple, they can’t actually get into that backup without your password. Meaning (again, if you believe them) this would be as safe and secure as shipping your own phone cross country after rebooting it.