Karatepe wrote:

And how on earth did that light house keeper manage to survive the
tsunami when the wave was estimated to be 40m high?

It's only water. If he survived the surge and was not battered by or
against something solid, it's only a matter of holding your breath.
Even if he had his lungs compressed, the frequency of a tidal wave
might have given him a few minutes to half an hour before the next
wave.

Most people that are hurt are trapped in the melee or carried out with
the debris. The chances are he was carried clear across the shoreline.