Back up question

Hi, ive backed up my library. Its only got 300 tracks in it, but it saved them in a matter of seconds. How can it possibly back up 300 tracks in a few seconds?

I ask as i just had a few issues and was trying to add my library to an older version of Rekordbox, and although the library said its saved, when i come to try and restore it, it says it cant restore? and thats what mamkes me wonder about it saving a library so fast?

thanks