After wiping free space on hard drives/USB sticks with FAT/FAT32/exFAT file system, I run Recuva to perform a deep scan and still retrieve large numbers of deleted filenames and folder names.
You're possibly looking at the file and folder names held in the File Allocation Table. These will not be overwritten with WFS. In Recuva Advanced Mode have a look at the file header pane. If it shows zeroes then you're all right. If it doesn't, have a look at the Info pane to see if it's been overwritten by another file. That's all right too.