That means if you're quick, you stand a chance at getting the files back, but you do need to get started as soon as you can and use your computer as little as possible in the meantime, minimizing the chance that any other files will take over the same space the old files took up.
It's not until that new data shows up that the old data is kicked out. So if your hard drive is a block of apartments, your deleted files don't get evicted, but their flats are marked as vacant for other files to move into. When computer systems delete files, they don't actually erase the 1s and 0s of the data, they just mark the space as free for new files.
