you're giving the coyote too much credit. Yeah, they're smart and cunning and got a nose that puts the whitetail to shame, but to steal a line from a good friend of mine, "calling coyotes is like checkers, not chess, don't over think it."
Coyotes will come to sounds that don't even sound like anything they've ever heard before. Take the twisted syco Verminator call for example. Blow that thing and it makes some crazy sounds, like nothing I've ever heard, but yet coyotes come. They are hard wired, they don't stop and think is that a cottontail or a jack rabbit or a deer. Instead, they hear distress. And I'm not saying they won't recognize a rabbit in distress sound, but what I am saying is don't think because it's not a sound that they've heard in the past that they won't still come. Why they stop sometimes, or why they run ya over sometimes has lots of factors involved. Once someone figures out how to make them come running every time, they'll be rich.