It depends on the school, but nutrition is becoming a recognizably important part of our education. I may be personalizing it, but I find that when people on the internet say "vets don't get any nutrition education" what they mean is that veterinarians usually don't agree with them about nutrition.
I think that veterinarians should respect the choices that their clients have made about things like nutrition, so long as there is no sign that it is harmful. In that way, I'd say that it was probably an oversight that your rottie didn't get his preferred food, but that I would have been apologetic that we didn't make sure that he got what he was supposed to get. If anything, it's a sign that procedures in the boarding facility are somewhat sloppy.
I have found that, when it comes to medicine, lay people on the internet go crazy about the one or two dials that they can control. Where there is scant evidence that "grain free (but potato loaded)" diets are any better than standard dry diets, there will nevertheless be people on the internet proclaiming that this is the single most important thing you can do for your pet, more important than regular exercise, awareness of behavior and signs of disease, etc. We find that the majority of our patients do great on a high-quality, highly digestible diet from a reputable source that has been shown to provide complete nutrition, provided that they get plenty of exercise and are not overfed. Nevertheless, if I tell a client that their preferred food is made by a manufacturer that has had serious quality control problems in the past, I can often expect to hear that I don't know what I'm talking about.
I consider it to be an example of the "bike shed" problem. If you submit designs for a nuclear power plant to a lay committee, they will spend hours discussing the appropriate location, size, arrangement and color of the bike shed, because that is something they can understand. The actual reactor design is presumed to be well understood by the appropriate engineers, who would have told them if there was a problem.
Similarly, I almost never hear on the internet discussions about why it is very important to go to boarded specialists for things like orthopedic surgery, or which procedure is more appropriate for which case. Instead, the discussions are all about food ingredients and supplements, things that lay people can grasp and which are usually harmless when changed. The other dominant type of discussion is "X killed my dog", which is a minefield.