I mean, why wouldn't it be? Most post-game elements (in pokémon games) aren't canon (just look at B/W). Also, there's the fact that all gym leaders look exactly the same. Even Tate and Lisa. And they're supposed to be KIDS. That's not all...exactly WHY is Giovanni there? He's supposed to be a wanted criminal. He's not even a gym leader anymore.
There are a lot more reasons, but it's all pretty redundant at this point.