I'm writing a thesis on horse_ebooks (because of course that's what I'd be doing), and one of the possible avenues of approach I'm investigating is Bakhtin's notion of genre. Because you are interested in the Horse, I'm going to share a few notes on this notion with you. To further a common understanding of the situation.
A classic understanding of communication and utterances is that someone wants to say something. They have some inner thought or emotion they wish to express, and in order to express it they turn to language. Using their understanding of grammar and their available vocabulary, they effort to produce some discourse that will hopefully convey the message across to the listener. It's a directed process, from one self to another.
Bakhtin is not a fan of this classic understanding. Rather, he proposes we understand communication in terms of genres. While it is true that communication takes place between individuals, it's not a question of one person talking directly to another person. Instead, it is a question of a person in a particular situation talking to others who are also in the same particular situation, and this situation has distinct and non-subtle effects on how the things being said are interpreted. The situation is as much a part of the communicative effort as the individuals in it.
A trivial example of this is a wedding ceremony. Everyone gathered has a certain understanding of what is going on, and unless something out of the ordinary happens, the situation will unfold as expected. Everyone knows the genre of wedding ceremonies, and this knowledge informs how those present understand what is occurring there and then. And, conversely, that it'd be weird if someone would act in a manner not in accordance with this genre.
Someone suddenly standing up and giving a rousing oration on the need to lower import taxes would be extremely out of place, and possibly cause a minor scandal. Whether or not there's actually a need to lower these tariffs is beside the point - there's a wedding going on, after all.
This kind of situational awareness is not unique to weddings, to be sure. It goes for all social situations, in general. However, there are only a certain number of such situations, and most of them tend to resemble each other over time. They become genres, albeit informal ones, and the understanding of those present informs what can be said in future such situations. If you are able to mobilize an understanding of the relevant genres, you will be able to make things happen in future situations pertaining to them.
The next time you hear someone relate an anecdote of someone acting strange at work, then they are giving an account of someone not understanding the genres at work. There is a certain expectation of how people ought to behave, and someone didn't act in accordance with these expectations. To amusing or confounding effect.
I imagine you might be thinking to yourself - how does this relate to the Horse? Which is a both understandable and crucial question
Remember how Bakhtin wasn't a fan of the classic understanding of communication? How it's not about one person saying something in a void, but rather a process of shared understanding of specific situations?
This becomes relevant in the context of the Horse, as it becomes meaningless to analyze it in terms of semantics and intention. It does not try to convey some sort of message, and decoding what it might be intending to communicate is a pointless exercise. It is communication without a subject, as it were.
Yet, it has over a hundred thousand followers. Clearly, it accomplished something with its tweets. And my hunch is that Bakhtin's notion of genre as social expectations might help uncover what this is.