I would probably be a little pissed, I wont lie, but at the same time as an artist a huge part of exposure and getting your name out there comes from the sharing of the work, I definitely agree the artists should get credit, but Ive had this happen to me so many times on FB for example, my images get shared and no credit to me, or when I google my art I find people claiming its theres, so I always try to clear up the misunderstanding and ensure I'm given proper credit, but inevitably its gonna happen, especially with something that is so in your face like a mural, and a lot of times its hard to find the artists name on a mural or they don't put their name on it, so that is tough sometimes too