All my deleted photos on camera roll came back

Hey!

From October until November this year I started to clear up my camera roll by deleting thousands of photos (around 10 000). It took a lot of hours to do that so you can guess how surprised and annoyed I was when today I realized that every single one of the photos i carefully took time to delete - had suddenly all come back to my camera roll. How in the world is this possible? I barely even have wifi here so can it be that iCloud brought them all magically back or do you any idea what happened?

The exactly same thing happened with my friend a month ago so we were just wondering how can we get rid of these photos again without having to delete them once again one by one?