For the observers, we can tell that the math has been off by a decimal, but that's not actually stupid considering it is still applied math, and yet a common mistake.
You don't have to be a BFL fan to be shocked and amazed that someone doesn't know how many billions make a trillion, and then ask how his math is wrong when he "removed two zeros".
The math isn't the issue, it's the persistent trolling from the person that attracts critical responses from others. If he didn't troll, the math would be corrected and glossed over, the thread would move on.