Lightning can actually strike twice. There have been instances where lightning has struct twice. Fun fact: you have less of a chance of winning the New York lotto jack pot than getting hit by lightning, twice.
It is recommended that you don’t take a shower after because the food is in your stomach and when you take shower there is water hitting on outside of your stomach that can make some people nauseated. Also, water permeates through your skin as well which might cause some issues to some people during digestion.
It might be true since when you are swimming in salt water you are bound to ingest some in your body. Depending on how salty the water is it can actually cut through phelgm that might create the itch in your throat hence coughing.
I have a feeling this is a myth…but a reasonable explanation could be that your body requires energy to digest the food so it could possibly divert the energy in mantaining body temperature while you shower instead of digesting food.