Is this related to WW1?
Was he writing in chess notation, which was mistaken for a code?
This happened in an episode of Foyle’s War. Could have been inspired by a real event.
Does the concept of throwing a bottle into the ocean factor into this?
Or if not chess, then writing about something innocent, and it was mistaken for code.
Yeppers.
Nope.
Nope.
Yes, so just tell me what it was and this is solved. Should be easy.
A to-do list?
A poem?
crossword clues ?
Nope
No
Was it musical notation?
Was it shorthand?
Was it a drawing of some sort?
Was it a language other than the one commonly spoken where he was?
Was it mathematical notation?
Was he writing about the location of ships he saw?
Yes and this little one was apparently too easy for you all.
Ralph Vaughn Williams sat down to write down a tune that he had in his head and did not want to forget. Everyone was very much on edge and looking for anyone giving codes or information to the enemy.
A boy scout nearby saw what Williams was doing and did not recognize the musical notation as any kind of writing he knew. He basically put him under citizens arrest and took him to the police, accusing him of sending writing coded messages for the enemy.
The police let him go. With a warning. 
This was called a “spy scare” and it swept over a lot of people.
You can read about this incident here:
One of the deadliest reptile encounters in history took the lives of 20 people. How?
This one falls under the category of 'if you heard about this story, keep your yapper shut". 
Was it a single reptile? Multiple?
Was it a snake? Crocodilian? Lizard? Turtle?
Were the deaths caused directly by the reptile?
Was one person killed by the reptile and then 19 died as a consequence of their death?
Nope.
Did THEY eat the crocodile and die of food poisoning?
Would the deaths be considered accidental? If yes, was the accident precipitated by their trying to avoid the reptile?
Was it a vehicle accident?
Maybe caused by a driver trying to avoid an animal in the road?
Was it a crocodile? Alligator? Caiman? Gharial? False gharial?