Can items backed up to the time machine from one computer be sent to the other computer by accident?

i have 2 apple laptops backing up to the same time machine. Can photos or other items backed up to the time machine from one computer be sent to the other computer with out permission or by accident?

it looks as if some items have gone from one to the other and i just want to be sure that it is not from the time machine.

Cheers

[Re-Titled by Moderator]