Yeah I did read the original post on the Aussie forum, but I still think that the pH 1 is incredible for nitromethane production. I would tend to lean toward contamination at a the local packing company.
I don't think it would be at the chemicals manufacturing plant because such a high acidity will have a knock on effect on the overall plant operations. Pure nitromethane is however acidic, not neutral.

This however is an important post because nearly all fuel that we buy uses imported Nitromethane thats blended locally by a chemicals company that will also blend other chemicals. The opportunity for cross contamination is high if the facility does run-down blending and utilises the same piping for the other chemicals products. You think its unlikely that mistakes can be made but I have seen it at large and small operations.

Just a point to note: Any fuel is either slightly acidic or slightly basic. It will never be neutral. Hence most fuel companies whether gasoline, diesel or Jet (Kero) or oxygenate type fuel producers, add stabilisers to the fuel to limit the corrosion properties of the fuel as well the fuels own affinity for oxidation.