I assumed it was something like that, but I didn't know enough about Nosepass and Probopass to say for sure. That is quite fascinating, though-most Pokemon have very straightforward methods of evolution, but some of them are downright bizarre. This at least seems to have a logic to it rather than seeming totally arbitrary, but I'm somewhat baffled as to why some Pokemon need to be traded to evolve, particularly given that there's rarely anything about them that would justify it.