The coyote was probably sneaking in and trying to wind you and when you went from your eCaller to the Howler he probably spoted you and took off.

I personally use .243 Win for coyote but that is just me - i know a lot of people who swear by .22-250 - there are a bunch of good calibers for coyotes. I have never used a .204 so I really couldn't say on it.