That does tend to be the case. Smoke delivers a small enough amount per unit time, that lost interest will terminate the consumption before it becomes acutely hazardous.
With modern vaping, the same thing should be true, without the smoke pollutants problem.
It might not have been the MJ component that did it, however. They said it contained MJ, not that it was entirely MJ.
It's more than that - they've tried in the lab to establish a fatal dose of THC for larger mammals (dogs, monkeys) but were unable to kill any. Any lethal dose of THC is an extrapolation from intravenous administration to mice.