CA,
You are referring to eid echad ne’eman bissurim and then you ask “If a mashgiach isn’t sure that what he sees is a bug so he says to himself “eh I don’t think it’s a bug” and passes it (but really it is a bug)”. How is that eidus, if he says he is unsure? I have never heard of an eidus where the eid says they are unsure.