To be fair LDB does not have it quite right either.
1. you delete a file - this causes the file's entry to be deleted, and it frees up the space that that file takes. makes it available for other things to be written in that space.
2. But the data does not go away on it's own.
3. when new files are written, they can be written anywhere on a drive. maybe overwrite the space left by (1), maybe not. It's totally random.
But entirely possible that 'deleted' files remain intact for years without being overwritten.
It's such a well known thing that there are 2 types of programs written to deal with it.
1. Eraser programs - those that overwrite the files or 'free' drive space with random junk. To cover over any deleted files.
2. Undelete programs. To pull back files that aren't overwritten.