There's a kind of a conservation law. The test they're using is probably very sensitive, which means it's likely not very specific -- that is, it may be sensitive to closely related coronaviruses. So a borderline positive may not indicate SARS-CoV2. All of the inconclusive tests they've had so far have been negative.
They keep saying players (plural) have borderline tests. I think they don't want the Storm playing down two or three players. Also multiple inconclusive tests make it more likely that there really is a positive, and if someone on the Storm really is sick, they don't want them exposed to other teams' personnel.