re: Exponential growth.
The article said they had botulinus bacteria not the toxin so we don't know if they could weaponise it or not. This is found in the soil everywhere, having a vial of it is irrelevant. If they wanted some they could probably get some bad chicken or even scoop up some soil anywhere. It's no smoking gun unless all bad food is as well.
If that's all they had then every third world country has the same thing in their soil. Bin Laden probably has some in his food right now, if he wanted to culture it. Having a vial of it might give them a week's head start.