[the Platinum Poppy]

Nah, it's not a prisoner's dilemma. Because:

Spoilers!

In a prisoner's dilemma situation, there's a pareto optimal solution that would have been reached if the prisoners would have made their decision together. I e, in the classic setting, both keep silent and both get off lightly. But since they're in fact deciding indepently of each other they won't do this. In the ferry situation, the Joker has set things up so that if both boats refrain from blowing the other one up, the Joker will kill everyone anyway. So the question there is: Trying your best to save your own skin by killing other people, or go down in a noble way? Pretty different. Sorry for lecturing, but I teach philosophy so I just couldn't help myself. ;-)