Given the question at face value, this is the only answer that makes any sense.

If a flash flood is coming, why would your family be any safer on one side of the river vs the other?

It looks like she/he was ultimately "walking away from the river" (and his family) on the first answer given.

True! I gave him 3 creative answers and the job required me to be creative. I felt I had shown that with my answers.

In hindsight, the office was shutdown and I would have been there only a few months. The scary thought is that he's out there somewhere continuing with this interview technique.