Truly there are a number of possibilities.

Perhaps the poor soul was, as Ramuh says, a wretch who believed he was the bomb.
Perhaps he was a bomb who merely had a chance of detonating.
Perhaps he was a bomb that could only be detonated with a night kill, rather than a lynch.

We will never be enlightened about this matter until the End of Days, however, so I deem it a futile endeavour to speculate.