The parent commenter is suggesting the random file may be malicious, not that their unzip utility or pdf viewer is untrustworthy.
They are further suggesting that the data contained within the zip could be distributed in a fashion that is less commonly weaponized (PDF is a common attack vector, zip is a common obfuscation method).
>I might have agreed with you 15 years ago, back in the age of antivirus and such.
What does this even mean? You still need antivirus today.