As mentioned by Drew, the files in question are auto-save files, which are distinct from backup files. Unfortunately for some reason, there is no index entry for # pointing to Auto Save Files in the emacs manual, hence my confusion.
My solution was simply to also change the location auto-save files are saved to, namely a hidden directory in my home ...
The Emacs manual (C-h r) is your friend for such a question. Use i in the manual to look something up in the index. For example, i auto save lets you get to node Auto Save, and the first item in the menu there takes you to node Auto-Save Files.
There you get a complete description of what these files are, what they are for, how to recognize them, how to ...
I don't know if there is a "correct" way to make this happen.
What comes to my mind is:
(defvar my-auto-save-regexp "/jdigit")
(defun my-auto-save-mode-fn ()
(when (string-match my-auto-save-regexp buffer-file-name)
(add-hook 'find-file-hook 'my-auto-save-mode-fn)