It took me a while to even realize that my sms app is "Google Messages". So Google talked to Samsung and said "yo, you doin anything with all those sms? lemme take care of it.
None of your SMS data is encrypted anyway, all of it can be obtained by your cell provider or the recipients cell provider. TBH Google is probably the least of your problems with regard to SMS safety. I had a friend who sent an invite code to some gambling website to her husband, so she could get promo credit, and AT&T flagged her text as spam and blocker her across their whole network for a week or annoying period of time.