Photos shared from my Mac

I have a MacBook on which I store all my photos (from my camera and iPhone) using Apple's "Photos". Me and my parents started using family share, which worked out just fine until now. I found out that pictures from my Mac (which I never sent by email or whatsapp or anything) show up on another family members iPhone. We did not activate iCloud Stream or anything that would suggest that photos from my Mac would end up on somebody else's phone. I also checked all my settings and could not find out what was going on.

Does anybody have an idea?

Thank you.