Probably a rather small deal at that age, and completely innocent as well.It shouldn't be a big deal. I remember having erections, very hard ones at that, when I was 5 or 6.
When a five or six year old has one, even a very hard one (seriously?), it's not going to offend anyone -- when a fifty-five or six year old sprouts up at a nude public spot and just smiles about it, the man's intentions - as in why it is being left on display - will be questioned by the parents who see him stiffened up near their little ones playing in the surf, dontcha think? What family social nudists have against erections left out and throbbing is when a guy thinks it's a god-given right for him to show off his proud peter wherever and whenever it comes to visit. So thanks in advance for understanding that such thickening occasions need to include a towel to pull over it, or at least turn the fuck over, so the families don't have to bear witness to that inappropriate perpendicularity.
Next time, consider flogging the dolphin a couple of times before a trip to the nude beach. They don't call it "going off half-cocked" for nothing! Rub that bottle and uncork the genie at home first ~ do everyone at the beach a teeny-weenie favor. Fifty years of that thing hanging down between the legs should've taught the owner a few valuable lessons.
It all depends on the time of environment. Like in a family environment I would say it would be inappropriate to display an erection in front of mixed company. Age is big factor too. Young adults and boys should have a pass but they shouldn't flaunt their erection either. As a lad growing up nudist with my old man, he made it very comfortable for me not to feel ashamed nor embarrassed because I popped a boner for no reason.