I'm just gonna say, I don't think the Gamexplain guys are saying the CacoMallow stuff is fake because they have some sort of insider knowledge to the contrary. I think what's happening is a combination of the following:
1 - They have a lot on their plate in terms of their own video content, so they don't feel it worth their time to really dig into this. I mean, Pokemon Sword & Shield are coming out in little over a week and they have to play through it and do their review, Terry just dropped so they've had a lot to cover there, they have a podcast, they have all sorts of original content to produce. I wouldn't be suprised if they were just swamped and didn't have enough time to look into it more closely. When you have a lot or other stuff to do and a bunch of people are talking about this potential leak that at a surface level glance looks fake to you, you'd be hard-pressed to want to cover it extensively since that would mean time away from what you were intending to do (it's their job after all), so you produce a quick video on the matter discussing it to stop people from hounding you to cover it and move on. Doesn't even matter how good or well-researched your take is, addressing it at all should be good enough for these people.
2 - They make it a policy to dismiss every 4chan leak as fake regardless of how good it looks, unless there's enough to definitively support it. Given that they said both the Grinch Leak and the ESRB Leak were both fake kind of tells me that they (or at least Derek) operate on a "fake until irrefutably real" basis. For example, the Ken leak was considered 50/50 by them due to the unique circumstances surrounding it, such as the game not being out yet, or Moray Towers not having any ink on it, which would be near impossible to fake. The CacoMallow stuff, no matter how good it looks, there's no real smoking gun that could definitively prove it's legitimacy, and it could very well be faked since we have the game and there are very talented individuals who could totally fake something like this. And if they believe this could very well be faked like every other 4chan "leak", why even take it seriously?
Either way, their takes on the CacoMallow posts are absolute
and while I get where they're coming from, they could've done a much better job on it.