True.I don't believe you're giving Google permission to PUBLISH your photos. What Google MIGHT do is use the photos (and the tags you applied) to help improve the AI for automatic tagging or searching, but your information would not be visible or available to other individuals. Kind of like Google already does with email for spam filtering.
OTOH, it does get a bit creepy when you start tagging your photos for the facial recognition feature. I used to like this feature (Google even had it on Picasa way back when) and didn't think too much about it. However, now that our faces are becoming a biometric password as well, one has to think about the potential issues with the facial data owned by these data companies like Google and Facebook.