I find when asked "What tartan is that?" it is best to respond very briefly, "The Maple Leaf", or "MacDonald". The response will often be as it was last Friday, "Oh, I belong to Clan MacKay". The asker is being polite in much the same way as they might say "Isn't it a lovely day". There is no need for a lecture or justification.
Now, last Friday as well, I was asked by an acquaintance that I hadn't seen in over 35 years, "Why the kilt?" My response was a bit more lengthly, but still brief "I recently retired and now can wear what I want, when I want."
Sometimes I have been asked "Are you a Piper?" To which I respond, "No but I like Scots whisky."