Whatever you call it, it just doesn’t make sense. So let’s say the minhag is for women not to participate in kiddush levana because of a geder of tznius. Fine. In that case you have to say that kal v’chomer, the geder of tznius would also lead to a minhag of women not participating in any public gathering which is longer than kiddush levana, such as the examples I mentioned above.
I don’t know any woman whose minhag is to avoid barbecues because of a geder of tznius. As far as I know, this is simply not a practice that anyone follows. So why do we follow the minhag when it comes to kiddush levana, but not to other outdoor gatherings?