Yes that's a very unusual dream. And you can most often count on the subconscious to bend reality in strange ways during a dream! I have noticed one thing though. Quite often there has been a recent occurrence during wakeful hours within the last few days that was probably filed away in the mind somewhere. It might, for example, have been rooted in reading an article, visiting a place, doing an activity, having a certain experience, or whatever. Sometimes that memory acts as the catalyst or trigger to launch the dream. If the dream was vivid enough and you can remember it well, quite often you can discover the trigger factor in it that will at least account for its origin and link it back to real life. But the odd events within the dream are mostly the subconscious getting its exercise while the conscious has nodded off and cannot rationally intervene or control. Some of these dream scripts are so bizarre, there is no logical way to understand why they unfolded as they did. There are general categories of dreams though. Take a dream where you're preparing for a recital. For various reasons, you're falling behind in your practicing, or the results are not fully satisfactory. Then the climax in the script draws near--you walk out on stage wondering how you'll play your program, feeling a deep sense of unease and dread! This is an example of a "preparedness dream".
In the dream at hand, at some point you might have been thinking about repertoire, (given all you learn, I know for sure that you do that), Russian repertoire in particular. In deliberating and selecting music for your to-do list, you might have thought of some music of Shostakovich, a favorite composer, that you'd like to play, feeling confident that you could certainly do very well. Perhaps in that same instant or at some other time, you considered some music of Kapustin which you'd love to learn, but it also struck you as being far less accessible, somewhat forbidding, with some doubt as to whether it would be a feasible undertaking. Then advance into the future. You're asleep, the subconscious takes charge and finds its trigger. Your companion in the dream might by your own conscious mind, whom the subconscious might enjoy mocking while it has the advantage. That's why you do not recognize the companion. Nor can you cannot see your own brain for that matter. You find Shostakovich first, who greeted you in a jovial, outgoing and friendly manner. There's a connection and comfort level with him. But Kasputin in the dream was unrecognizable, inaccessible in a far corner, infirm, noncommunicative, thus causing you dismay and disappointment. The people tending to him might have symbolized other pianists. You would have liked so much to interact with him. So this visual dream script might have illustrated your own earlier rational thinking while considering new repertoire possibilities. That's my take on it.