You're right. We don't know any of that, which renders a statement like "A spoonful of the stuff in a city's water supply could be catastrophic" functionally meaningless.

You're hedging your speculation plenty with that phrase, "could be," but by putting what appears to be a dosage and delivery method in the same…

Unless, as completely made up, you put it in the water supply. Note that the New Scientist article did not mention its possibility as a waterborne toxin - that was Mr. Estes' confabulation.

According to the World Health Organization:
"Waterborne botulism could theoretically result from the ingestion of the pre-formed…

The genus Clostridium consists of strict anaerobes, meaning that they cannot grow in the presence of oxygen. So in terms of a natural outbreak, it's not really a grave threat.