There is an old story told about how most drowning victims are found with their fly open... drunk people peeing into the water slip and fall into that water. I don't know anything about this particular incident, but peeing off a dock or over the edge of a boat is always dangerous. You are doing something very routine at the point where land meets water. Even without alcohol/drugs, overconfidence with a routine task quickly leads to big mistakes. (I saw similar incidents with people who decided pee over the edge of cliffs. Don't do that.)