Alex, a few possibilities comes to mind. Sometimes, I prefer to buy plants that are not ready to bloom, or already in bloom, when purchased. This includes fruit trees, perennials, and even veggie plants, like tomatoes. Blooming causes a certain amount of stress on plants. Flowering is a reproduction process,, which often leads to seeds, can be likened to pregnancy, and childbirth, in animals, that results in offspring. Transplanting, is yet another stressful process for plants. Some plants don't like being transplanted, period, and will sometimes die, simply for being moved. So, your Rhody was possibly undergoing two or more stressful processes, at once.
This is another reason why I may not immediately set out plants, that I just got, either from a local nursery, or through the mail. They often need to get adjusted to conditions in your garden, first, before being set out. Many mail order nurseries suggest you ease the transplant process, by leaving the new plant, in shade, for a week or two, and easing the plant into conditions it'll be living under, like sun, rather than immediately setting out, because it had been traveling for several days, in a dark box, and possibly tossed around, by handlers.
Was there a frost, since the plant was set out, Ora lack of moisture? These could also create an element of stress.
Other than that, I think your plant is healthy, overall. It may bloom normally, beginning next year, after it adjusts better to your yard.