Was that a MissingNo reference?
There are many games with unused items that could still have some reference here and there, as in, it calls an existing ID that was thought to have been removed or is "soft removed", as in, an item with an id, registered with something like "status=false", but the event that is triggering it just calls for the ID without checking its status.
If you want an example using Pokemon, I'm pretty sure that there were some memory manipulations that cause something like an item slot to be registered to some item, or to multiply it with a certain amount.
Pokemon's MissigNo is the reverse, it's when the battle event calls for a pokemon, but the ID is invalid.
Ex: Let's say that in the first game, there are 151 pkmn registered, each one with an ID that fits in 1 byte (0 to 255), so 0 to 150, but you use memory manipulation or a bug, and it tries to call ID 200, which doesn't exist, but there is no error treatment. That's Missigno.
However, let's say that in the original game, there were actually excluded pkmn that were never activated in the first place, and they go from ID's 200 to 240.
If the event calls for an pkmn of IDs 151 to 199, or 241 to 255, it will lead to Missigno, but if it were to trigger 205, that would lead to one of these excluded pkmn that could be incomplete or bugged out, but is an exiting entry.
So, not all bug references are a Missigno reference, I would argue this manga is influenced more by Soulsborne bugs mixed with random JRPG games.
