Ah didn’t realize you were actually using slackware, my bad, I thought you were just referencing the slackware approach of a full install
Also I would not assume that deleting them and renaming them has the same effect. Unless you’ve seen the source code and can confirm how it works, the pattern matching for files could be something that looks for anything in that folder, or anything containing .desktop (if you renamed them like .desktop -> .desktop.hidden)
Based on a quick Google search it’s a bug in KDE, and even uninstalling the application does not always remove it from the menu.