Its because that pet is not treated as purple, but as green quality, despite the description font color:
Keshian Panther can be Summoned at Pit Arena Gladiators: rank 1 (purple pet?). Summon/rewards as Enchanted level pet as well. Here is the comparison:
Stygian Spectator shouts: All hail Dimunconq the slayer of Keshian Panther.
You gained 62400 XP towards your Mastery Advancement (+30% membership bonus).
You’ve received 1 Gold, 50 Silver!
You have gained 5417 faction standing points with the Pit Master’s Arena (Gladiators) (+30% membership bonus).
Pet: Polar bear - Enchanted Pet
Stygian Spectator shouts: All hail Dimunconq the slayer of Polar Bear.
You gained 68640 XP towards your Mastery Advancement (+30% membership bonus).
You’ve received 1 Gold, 50 Silver!
You have gained 5417 faction standing points with the Pit Master’s Arena (Gladiators) (+30% membership bonus).
Mastery different due to extra 15% pot running 2nd fight.
This is still not fixed? It’s being sold for 25g at the trader like any other epic pet but it’s a green pet in the arena… Best 25g spent ever, twice now because I forgot about it after a while