In other words you know to not act means life and to act means death but the saving of 400000 people, but you have no time to ponder the implications either way, in fact the decision must be made practically instantaneously and instinctively, and then of course what I said above also follows.
In essence is this a selfless act?
Ie it is not motivational exactly, it is just reflexive action.
You still have the notion of consequence of action here. The consequence seems to be driving the action and thus appears to be motivated by the perceived consequence of saving400,000 people. So, it is still a matter of motive ie: how good it feels to save 400,000 over how unknown and scary death is going to be.
The motivation of a fear of the unknown (death) cannot overrule the immediate motivation of knowing (known, [primarily examplified in Bruce Willis movies]) how good it will feel to save 400,000 lives.
How can a person be so selfish as to save 400,000 lives then die as a result of their actions?