It's just a semantic paradox. Some dictionaries refer to a skirt as an exclusively female garment and a kilt as an exclusively male garment. Given these parameters, you could not logically say a kilt is a skirt. Other dictionaries, define skirt as an un-bifurcated garment without specifying sex. In this case, you could refer to a kilt as a skirt.

Words don't bother me; I am not offended if someone calls my kilts skirts. On the other hand, I am offended if someone doesn't recognize my kilts as male garments.