I have to congratulate your observation skills. Bravo.
In the end, have the question received the definite answer? I checked QNAP forum and there is no answer too.
So, is it false positive or is it genuine issue?
You had 2 years to think about it, as you have noticed. Do you have an answer?
Does anyone else?
Can Sophos AV be installed on the QNAP system?
I didn't mean to be offensive, but there's a big chance the original poster will not see your reply or even know about the answer anymore should there be one.
It's most likely not a false positive so I would check your NAS. Don't know whether you can or cannot install Sophos AV to it, but you can also scan all it's files from a workstation connected to it and I believe QNAP also has a virusscanner built in to its firmware.
And no, I didn't have 2 years to think about it since I have never seen this thread before (or at least do not remember seeing it before). Anyway thanks for the congratulations.