Seems to me like this would be incredibly awkward, but then I'm not a nudist (except on very special occasions, like Thursdays). Maybe to them it's no big deal.
It seems likely, though, that the citizen arrested in this citizens' arrest was not himself a nudist, although he was in fact nude at the time. I infer the former fact because they arrested him for allegedly filming them with a camera he had hidden inside his esky.
Oh, "esky" is Australian for "beer cooler" (as non-Australians may recall from this post about a bloke who got a DUI for riding on one)—makes the previous sentence a lot less creepy if you know that, I guess. It also means that his filming activity was less obvious than it might have been.
Still, sunbathers on Maslin Beach in South Australia noticed the man "positioning his esky to face other unclad people on the nudist section of the iconic beach," and became suspicious. An investigation revealed that he had cut holes in the side of the esky through which he was apparently recording their nudeness. (This is why I infer that he wasn't a nudist himself, because if he were, he wouldn't have found this worth recording.) According to the report, he was then "confronted by nudists," which may have seemed like a dream come true but quickly turned into a nightmare as "[a] group of nudists then chased the man down the beach and made a citizens' arrest until police arrived."
Police examined the camera and found that no video had actually been recorded, so they decided that there was insufficient evidence for a charge of "indecent filming." Attempted indecent filming, maybe, but they let him go with a warning this time.
Because I know that, like me, you are wondering whether one could actually be guilty of "indecently filming" an openly nude nudist running around in a public place, I looked into it and have conclusively determined that the answer is maybe. Under Section 26A of the Summary Offences Act, as amended by the Summary Offences (Indecent Filming) Amendment Act 2008, "indecent filming" means the filming of:
(a) another person in a state of undress in circumstances in which a reasonable person would expect to be afforded privacy; or
(b) another person engaged in a private act in circumstances in which a reasonable person would expect to be afforded privacy; or
(c) another person's private region in circumstances in which a reasonable person would not expect that the person's private region might be filmed.
"Private act" does not apply here, but "private region" certainly does. (That is, it doesn't mean, like, your backyard.) It is, however, a defense to prove that the filmee consented, or that the filmer was "a licensed investigation agent" who was gathering evidence for a paying client. (Congratulations, private investigators' lobbyists.) Here, though, there is no evidence that the nudists consented to being filmed, and the pursuit and citizens' arrest seems to be pretty good circumstantial evidence they did not. Nor is there any evidence the filmer was a P.I., or if he was, he was filming on his own time.
So this seems to come down to whether a reasonable nudist "would expect to be afforded privacy" on a public nude beach, or at least would not expect that his or her private region might be filmed there. I guess I would say the answer is no, unless maybe Maslin Beach has signs posted saying that filming is not allowed. That is entirely possible but I don't know the answer. (Note to self: try Google Street View when you get home.)
Hopefully we can have this cleared up before the start of the annual Pilwarren Maslin Beach Nude Games, which are set to begin next month. They could just ban eskys, I suppose, but I seriously doubt anyone wants that.