either you have a unique bug or you read it wrong.
you normally get 10% of their lifetime take when you defeat a named pirate.
Never heard of it being otherwise except maybe for random bugs.
In this game gold has neither weight nor volume, and it can be used to feed the crew.
Ok, it doesn't feed the crew, they look at the nice shiny coins, smile and exist without food providing you have enough for each crewman to dream.