You could try (try!) to argue that its just hobby photography, and that your Nikon isn’t anything more than a holiday camera.
But if they keep persisting , you have to judge how hard you want to fight back. Be sensible in this, and sont ruin it for other photographers:).
'no commercial photography ’ doesn’t mean anything about what gear is used, but non-photo people still see any kind of ILC as ‘a serious camera’ and this equal it to commercial photography in this case.
Heck, some people get ‘scared’ of it, thinking about privacy.
So argue a bit that a hobbyist camera doesn’t make it commercial photography, but I wouldn’t put up to much resistance if they don’t listen to it.
At baby swimming taking pictures / videos was allowed , so all kind of moms in the pool with their newborns , and dads on the edge with smartphones.
But if I take out my m4/3 camera with an effective 35mm lens I was immediately asked to put it away. ?!?! . I can then go argue that those smartphones take better video in the low light of a pool anyway, but if everyone is looking at you weirdly , it’s just better to put it away and let it blow over .