Just to be sure--you're not looking at the Recent Calls or Call History section, are you? It just seems odd that your recent outgoing calls would be added to Favorites.
I recall that on other phones (I think my Nexus 5), the Favorites screen also shows recent contacts as well. It's that the Favorites are listed first, and if you scroll down, then you see your most recently called contacts. Is that the case for you?
Just checked my Nexus 5--I was mistaken, that phone's dialer separates the Favorites (Speed Dial) from the Recent Calls. I may have been thinking about my old Razr Maxx, which is now kaput.