I'm a little in the dark about this "language" stuff. I think a bull's bugle means, "Man am I ever horny!" His other vocalizations are ways to emphasize that point. I think, like with deer calling, a lot of this stuff gets overinterpreted.

There is a very good and sufficient explanation for why it all gets overcomplicated. First, we love the chase, and when people love something, they tend to imbue it with all sorts of mystic qualities it may not actually possess. Second, we fail a lot in our chase, so we need all the excuses we can grab. Third, and by far most important, is that there is big money to be made by inventing new, previously unrecognized game vocalizations. When you do that, you can then be the sole provider of the correct gadget that makes this new miracle sound.