Apparently more people eat their tobacco cigarettes when a police officer is walking up to a car than eat their marijuana cigarettes.
Clearly it isn’t one time consumption. Cumulative effect has to be a part of their ‘statistic’.
The article states that the ratings in the article are based on the ratio between a typical dose of the drug in question and a fatal dose.
So no, this particular study does not take in to account cumulative effects. And the article states as much.