I agree that's plausible speculation, but it's still speculation. It seems like a pretty serious failure of media literacy to assume that these screenshots are authentic without any concrete knowledge of how their authenticity was confirmed.
I'm not sure it's in TechCrunch's interests to tell us how credible their leakers are. Leakers probably have repeat value and they don't want to poison their relationship.
Given how few people presumably have legitimate access to these, Techcrunch probably couldn't say much without risking identifying their source. When people leak to media, they often do so on condition that they won't be identified.