Continue your quote - What's the very next line, in the same paragraph even?
> ... because the leaked documents have arrived in the form of photographs of printed documents, rather than original files, the possibility of forgery or alteration must be considered.
And you may have misread that other quote you posted: It's saying the documents "have the appearance of tampering."
They also questioned the authenticity multiple times, making it very clear that authenticity had not been confirmed:
> Though they resemble those described by the Times, we can not confirm their authenticity.
And again, further on:
> If the documents were partially faked, were they disseminated to help Russia advance its public relations goals, perhaps by minimizing their casualty numbers or inflating those of their foe? They certainly would not be fooling anyone at the Department of Defense, since they obviously have the original files on hand.
... Looks to me like they reported the news accurately, making no claims about authenticity whatsoever.
The only significant difference I can see between that article and CNN's reporting of the same day [0] is that Grayzone actually showed the documents.
0 - https://edition.cnn.com/2023/04/07/politics/ukraine-document...