The lack of standards falls on the acting part. I ran a quick search and found that SWGDE best practices guides and documents do consider the case for the presence of malware on the digital evidence sources on many different scenarios [1]. Having an "expert" who is unaware of these guides is another story.
[1] https://www.swgde.org/?swp_form%5Bform_id%5D=1&swps=malware