I have the same vehicle and I had this problem for a week or so. I know not to get rainx on the mirrors but it happened anyways when I mixed up my MF rags (could stand for “microfiber”, or an expletive). New car, and it looked kinda like yours— not a good feeling. Anyways, I’m on board with your theory that someone at the dealer hit it with a chemical that they shouldn’t have. I’ve seen some serious [screw]-ups from dealership detailing crews.
For my situation, I read up on removing rainx and I hit it with some ISO (I forget if it was 70 or 90%). Knowing how relatively “soft” the side mirror glass is, I scrubbed at it with the ISO but I was VERY careful. At first it only looked slightly improved, but after it either rained or next car wash, it pretty much went 100% away. I might’ve completely forgot had it not been for your post.
RainX is unlikely to be what the dealer used, so take this advice knowing the issues *might* be similar but different.
Hope this helps at least somewhat. You’re at least not alone.