It seems some people here again blame the victim (all too typical these days). You imply that if one goes nude on the Dutch side, you should expect "bushwackers" to pay you a visit.
If the OP had been fully clothed, and just there with the family to sight-see, would it have made the "wacker" any less obtrusive? For whatever the reason, those people do what they do for an obvious reason, and we should not "blame the victim" that was unfortunate enough to experience his behavior.
As the OP later stated, this post was for a heads-up to anyone who may visit the Beach to be prepared for something like that to occur.