I can not see it being real. The thing about that leak is it takes things that we already know and repeats that information, but that’s about it.
We know there’ll be new cutscenes, we know there’ll be a new Keyblade, we know there are other playable guardians of light etc. so it doesn’t go out of its way to get into specifics in order to make the other stuff, like a twilight town mini-game, seem plausible.
I also don’t think that such a direct file size can be known for a DLC that would be releasing in 5 months. Price, yes, but they’d still be working on various things and optimisation that such a number would be in constant fluctuation.
Like prior to KH3’s release, people jumped on fake rumours and spoilers and believed in them so much they accepted them as truth despite evidence to the contrary. I really hope we don’t have a similar situation in the lead up to the DLC. Discussion and theory is always fine and welcome, but blind faith in something that people have pointed out as incorrect is exhausting. Debate the contents of that “leak” to your hearts content but I really hope no one hangs on to it and, when Remind releases, isn’t like “This was support to have a mini-game in twilight town and there isn’t one! Worst game ever; this is so disappointing and the devs were lazy for not including the one that I read about months ago from an unverified source.”