Two Telling comments? The Answer Perhaps?

[OC Richard]

The 'uniform' of the average Scot is pretty much the same as the rest of the world. T-shirt, blue jeans, trainers (sneakers) and given our climate, some form of sweater or jacket.

Yes here you see that too, but far more common is t-shirt, cargo shorts, and sandals/thongs/zorries/flip-flops (terminology differs according to where you live, here all such things are usually called 'sandals') and if it's a bit chilly a hoodie. I remember looking around the room at our pipe band practice and everyone was dressed like that, the only blue jeans being worn by our only Scot!

an assumption would be made that there was a reason for them wearing a kilt. Common reasons might be as follows:-

They are attending an event such as a wedding, Burns supper, ceilidh, Highland Gathering, formal dinner, etc.
They are a member of a pipe band.
They are celebrating a sporting event.
They are making a cultural/political statement ("I'm a proud Scot").
They are mildly eccentric.

That should be a sticky! That's awesome.

Using my Western Wear analogy, if somebody walked around here (SoCal) in full cowboy kit (hat, shirt, buckle, jeans, boots) we would assume
-he's visiting from Texas
-he lives on a ranch
-he owns/rides horses