Live @Vesko wrote, RxJava and event bus differ in their nature and may serve to solve different problems. Nevertheless, there are some scenarios in which both of them can solve the same problem (although at different costs), and this might be the reason for why many people confuse these two concepts.
RxJava is conceptualy similar to Android LiveData that was released not so long ago, and to better understand these concepts, as well as event bus, I suggest you read my post. In the post I go over these very concepts, describing the scenarios in which we should use one over another and the pros and cons of using one rather than the other. I think it may be useful to you:
When and why to use LiveData
