The fact its opt-out is sketchy too. As far as I know, there's no request for consent nor any acknowledgment its being stored in iCloud in the first place. Between that and the all-encompassing nature of Siri having access to app contents by default, not sketchy at all. Siri used to (still does) access encrypted email contents in Mail if you have that as your client but it probably does the same to those who don't uncheck it in iCloud AND Siri