At some point the evidence crosses the line of "beyond all reasonable doubt" and SARS-CoV-2 itself becomes the proof.
The virus was already looking suspiciously engineered, in ways that you wouldn't expect from natural evolution. It appeared right next to a lab doing virus work. Now there's a document saying they wanted to engineer a CoV in the exact same way that SARS-CoV-2 appears to have been changed. The question is not "did they get funding to do the work" at this point but rather "who funded it" (assuming it needed explicit funding in the end and wasn't simply creamed off another project).
But it's the first piece of concrete evidence that people were in fact doing what has been claimed.
Also remember that there are two virus labs in Wuhan. One is WIV, but the other is across the street from the wet-market (as I understand it).