This happened to me during a Google Takeout export when I was degoogling in late 2019. I recall going through some photos from the earlier 2010's and some random pictures of other people were popping up. About a month or so later I received an email from Google letting me know that some of my files may have been accidentally in other people's exports. Since then, I stopped using apps like Google Photos and cloud storage in general. If I do, my files will be encrypted before I upload them.
Here's the original story: https://9to5google.com/2020/02/03/google-photos-video-strang...