I got a similar letter from US Bank about 3 weeks after my car was delivered. (It looks like US Bank didn't even access my credit report until two weeks after I was originally supposed to pick up the car, so they wouldn't have been much help even if they accepted me).
I'm not completely surprised they turned me down as I had noticed that the questions on the application were about income, but I don't have much income because I am retired. There were no questions about assets, which seems to give them a rather incomplete picture. In any event, somebody else took me on, so no big deal.