The second image looks like a patch. I would ask for a second opinion. Or get the LBS to show you that other bikes have the same "feature" in person. Pictures can look deceptive. $13k is a lot of money if the bike is not perfect!I get the point about aesthetic design if the entire bike was like that but only the top tube seems out of place, hence my query. The bike is in a well lit room with roof windows where I prepped it for ride wrap, so when the sunlight hit it, I noticed, as you would when riding on a good day. The torch was only used to check over the frame for scratches defects etc, so not OCD by any means, but over here when you pay $13k for this bike I think its fair to check it over in detail.
The strip you mention, I agree in the sense that it doesn't look like a good bit of aesthetic design, whatever it is... Indoors you can't see it, but depends on the light intensity.