"men can't wear dresses" but they can wear kilts, not a dress, but a skirt at least.
My 4 year old gs was outraged when we were going on a muddy walk and I suggested that he wear a pair of his sister's old wellies, as we didn't have any others, they had an incy wincy bit of pink on them. "I just can't wear those, they're girls" he protested, I did tell him that no one would be looking at his feet and making judgements, fell on deaf ears, he wouldn't have it. Anyway I've bought him a suitably macho pair of his own with spacemen on them, only they could be space women, who's to know under the spacesuits they're wearing, but there's a blue background that's the main thing and no pink God forbid
A friend of mine lives in Brighton and she told me about a drag queen who resides there, the wonderfully named, "Betty Swallocks" perhaps that's who your grandson spotted NanKate