My fiction is for most people (but not me), RPG = a character in a fantasy setting (were fantasy = swords, knights, wizards). The end. By this they categorize both every console Zelda game and every Final Fantasy game as "RPG". But the 2 series are not remotely similar to each other. The Zelda console series are skill based action games with puzzle solving. The Final Fantasy series is a menu based choice game with possibly some strategy in which choices you make and what upgrades you choose.
You could probably also argue that The Witcher does not fit in the same category as Wizardry or the original Bard's Tale for similar reasons.
And, almost like trying to define "sandwich", if you pick some criterion then you can find examples of games that fit that criterion that most people wouldn't consider an RPG. Consider if you claim "Zelda" is an RPG because you move a character around a large fantasy world and have inventory then by that definition "Ratchet and Clank" is an RPG.
Further, even the term "Role Playing Game", in a racing simulation I'm playing the role of a race car driver. So technically PRG fits. Same for a skiing game or skateboarding game or many other games were you "play a role".
I'd argue game genres should be defined by how they're played, not how they look. As such, Wizardry, Diablo, and The Witcher do not belong in the same genre.