You need to differentiate between real champions and champion-like monsters. If it says "Adventurer" in the description it is a champion for hire. If it says "Creature - adventurer", it is a monster for killing.
So if he attacked you, it was the 'creature' one. You can tell by placing cursor over him - you can only hire those that show a speech bubble. If you cannot hire any in your game means you are only running into monster-ones, keep looking for the real ones.