[GAMEPLAY] Dragons don't get counted consistently for Cho'Gath's feast tool tip

I was playing a game as Cho'Gath trying to get a bunch of feast stacks so I kept checking the feast tooltip to make sure I was properly keeping track of my monster kills since only 6 count. While doing so, I noticed that when I killed my first dragon, both the dragon counter and epic monster counter increased by one. At the time, I guess that made sense because dragons can be considered epic monsters. Then I killed rift herald and had 2 epic monsters and 1 dragon on the feast tooltip. However, when I killed the 2nd dragon, only the dragon counter increased this time so I had 2 epic monsters and 2 dragons on the tooltip after killing 1 rift herald and 2 dragons. I'm not sure if the first dragon wasn't supposed to be counted as an epic monster or the 2nd dragon was, but there seems to be inconsistency in the feast tooltip's tracking.