The first is outraging public decency, and the second is indecent exposure.
In this situation, it is likely the man could be seen as braking either of these laws, due to the nature of the action.
Some viewers of the footage have tried to conclude why this might happen, with one traveller suggesting he may have been under the influence of alcohol.
Others questioned the actions of those around him: “Why isn’t anyone doing anything about this. Just sitting there watching??”