First off, I know how manga works. Second, I was saying the coat looks goofy as hell, as if it was either edited in BY NOT THE MANGAKA (editor, tl), or the mangaka did it as a joke. Look at this and tell me it doesn't look like a prank pulled by someone.
You are correct that the coat looks goofy, and I think that was the whole point. Evans was so obsessed with those price tags, that he needed an excuse for why he took it from a shop about to apply those tags to their new merchandise. The price tag belonging to a goofy coat was presumably to highlight how desperate Evans was at that moment. Under normal circumstances, he could've claimed he wanted to gift the coat to someone else, or he could've just returned the price tag with a simple "sorry, I misread the price" or similar.
But no, the editor certainly didn't add those swirls.
Not without the author's consent, that is. And I don't think the author used that pattern as some kind of meta joke, as you seem to think.
As for why the pattern looks like it's "edited in", that's because the pattern doesn't flow with the clothes. It's impossible to manufacture patterns that will fit an infinite number of possible 3D transformations, after all. While uncommon, it still happens even in works that are perfectly serious for perfectly serious reasons. Drawing these patterns by hand would solve the problem, but would also greatly increase the workload on the artist.
The most common example are when characters (usually female) are wearing fishnet stockings. Artists can't use the dotted patterns that always blend in, and must instead fall back to honeycomb or similar noticeable patterns. And that's when it becomes obvious that those patterns look pasted on.
At least this artist tried to ensure the patterns were properly scaled. I've seen artists that don't even bother, so the pattern looks comically huge when the character is drawn far away, and incredibly tiny during closeups.