Yes, obviously a judgement must be made, so a lone person, possibly a pirate, (who I believe aren’t much interested in cruise ships, anyway) is clearly not a threat in the way a boat load might be. But the judgement is not always easy. I have read of RN sailors scarred for life by the fact their ships, for the good but mistaken reason they thought enemy ships were approaching, left many sailors to drown after the Bismarck had been sunk.