> So it’s a false positive?

They already told you clearly, so it sounds like you're trying to browbeat them with a fallacy of equivocation over the scope of "it".

These things are not equivalent:

1. A biological test for a parasite in a sample of equipment/material from the factory. (Claimed as false-positive.)

2. The analysis of the supply-chain for the food that sickened people which led to that facility as a common factor. (Presumably still accurate.)

___________

To use a criminal-investigation metaphor: Suppose a dead woman is found covered in knife wounds, and the circumstantial evidence leads to one Knifey McStabberson, since he (A) previously dated the woman and (B) sent a death-threat once via text-message, and (C) has a collection of hundreds of suitably-sized knives. Investigators notice one that looks bloody, and test it... It's her blood! Wait, oops, no, false-positive, it was something else.

What is your takeaway from the story so far? Is it that Knifey McStabberson himself is "a false-positive" and obviously totally innocent... or is it that it would be a good idea to check more of the knives scattered around his house and in his car?

Christ, man, hasn’t the McStabberson family been through enough? Do you not have the decency to finally bring this witch hunt to an end?!