So, I suppose you shouldn't give your fake id (digital or physical) to a government officials. It also seems "obvious" that it's similarly unwise to give it to a bank. But you can do that to a random guy on AirBnB? A hotel? To a delivery service (Uber/Wolt/whatever)? Dicsord? Where is the line between a bank (a private commercial corporation) and Discord (a private commercial corporation)?
The "legal" line is usually around fraud - trying to obtain some financial gain by providing false information. There is nothing to gain by giving a fake ID to discord - but it probably violates some rules around unathorized access to computer systems.
Guessing they probably just ran some rudimentary OCR on the image to compare the name and DOB. I modified the actual license# as well as the picture.
Not having a correct photo or license number didn't really mean anything to them if their OCR didn't have any half-decent verification that would look at the fields where that information was expected to be, anyway.
But not even worth that effort for this. Not a subscriber, but probably won't ever use it again, either.