Whether people are simply naked in a sauna, or fully-signed-up naturists the point is surely still the same - if the culture in the place you are visiting is to be naked (be that for philosophical, societal or purely practical reasons), then surely the respectful thing to do if 'investigating' that lifestyle is to blend in with the accepted norm.
I understand from Swedish friends that anyone wearing trunks in the sauna would tend to be regarded with ridicule and/or suspicion. Certainly the couple of times I went to a public sauna in Sweden there was not one person being coy and staying covered up - and the same applied in the showers and changing room; swimming trunks only went on to go through to the main swimming pool, and came off again as soon as you returned to the changing room.
There are plenty of people the world over who may choose to go naked on the beach or elsewhere, but who don't in any way subscribe to the classic naturist philosophy - they just prefer to be naked. How should we refer to them? 'Naturists', 'nudists' or something else entirely?
Many poster on this thread seem to be conflating nudism and Swedish sauna culture. Just because the Scandinavian cultural preference to use the sauna nude it does not automatically follow that they are all nudists. A tv show about nudity in Swedish saunas is exactly that and should be viewed in that context. Just because some people are naked does not make it relevant in any way to nudism. The nudist movement would be in a much healthier state if people understood the difference.
I agree with you with what you wrote based on my own experience. The Japanese and Koreans also have their own sauna and they have been practicing this for hundred of years and I don't think that they are all nudist. As for my own experience, I was also very hesitant when I first step on the Onsen (Japanese Sauna) because I am not a nudist back then in 2018. My cousin husband (a Japanese man) brought me to my first Onsen experience and I voiced out to him my concern as I have not gone naked in front of anyone. He said that I will be fine and just follow his lead. SO went to the Onsen and we went to the dressing room and I followed his lead when he started undressing, so did I. we spent maybe 2 hours in the Onsen where everyone are naked. Funny is, one time I was Video chatting my cousin and her husband who brought me to the Onsen and got naked with me, just came out of the shower and was wearing an underwear and when my cousin told him that I am on the computer video chatting, he abruptly hid himself and I asked my cousin why and she said that he is embarrassed because he is half naked. I said, what do u mean embarrassed? We already saw each other naked in the Onsen and he said that is different. In the Onsen where nudity is expected, he said that when you go to the Onsen, everybody is the same. No rich, no poor, no good-looking, no ugly. Just to prove a point that not everybody that goes in the sauna are nudist like us.
I saw that and wondered why they bothered even showing it. I suppose that the segment might have upped the ratings by a few ("ooh, naked men) for the Beeb. The show is supposed to be about how our European neighbours deal with the aging process. (I think, or it might just be 2 middle aged guys on a jolly) Since social nudity is a part of the Swedish solution I think that they rather missed the point, even if "the rude, naughty bits" were pixcelated.