Shared documents between accounts on MacBook

Hi, I have a question. How is it possible that I download/upload something on my MacBook on my account and this document appears even on my girlfriend's account? For Example I've uploaded some pictures on my account and she later on asked me why I needed this picture for. ( I did a calendar as a gift for her). How is that even possible, that this picture appears on her account as well? Another weird situation was, that she came to me, that her iPhone shows her that she visited and spent some time on some website, but she can't be there because she didn't have the phone beside at the time. It was also me, when I've created the calendar. I really don't understand how this could appears on her screen time...

Just to be clear we have separate Apple ID. We have family sharing, but I think only for iCloud, I suppose it shouldn't share what we do on our accounts, am I wrong?

Thanks for advice in advance.

Lukáš