I set up Chrome remote desktop for a family member today, and absolutely sync is enabled simply by signing in. Sure, it presents "Undo" after the fact, but on visiting the associated Google account, it had already copied everything. I have NFC where this article sourced "sync isn't automatic", but it clearly is. Zero UI indicator it's happening until the Undo button appears, by which time you've already been ripped off.

Nice to at least see they're making it opt-out, but the damage has already been done.