The difference is there arent random natural sources of liquid radioactive materials all over the place that could cause a large scale leak and have humans randomly tapping on them and hoping they don't cause it to blow.

Maybe not necessarily natural, but I think you underestimate how much radioactive material is out among the general public (i.e. outside of power plants and missile silos). Radiology as a medical field literally revolves around using radioactive materials for medical imaging, and there have indeed been incidents where regular people got their hands on some canister of the stuff (that didn't get properly disposed of), oohed and aahed as it glowed in the dark and they painted themselves with it, and a week later dozens of people are dead and hundreds injured from radiation sickness.

Sure, my analogy is not perfect. But similar accidents have happened in the past (accidental leak of anthrax from a Russian lab, and voluntary leak of anthrax from a US lab).

I don't know if it actually comes from that lab. I'm just saying it's not a wild conspiracy theory to think that it might well come from there.