I'm currently running this adventure.
I think the temple was originally to Horus but all of his followers died and it was taken over by Exethanter who redesigned some of the temple adding the cursed obsidian statues and possibly even the large one in the center. This is because the temple is a mixture of Egyptian imagery in amber, white and gold; and wizard imagery in obsidian that acts mainly as traps.
Horus is some times depicted as a god of secrets, and there are some elements of his imagery in the temple. The amber golems have a very Egyptian appearance with hawk heads, which is generally how Horus is depicted. Additionally, the original wizards wore these very bright white and gold robes, which is heavily associated with Egyptian royalty and the sun - another domain of Horus. There are signs in the temple that its original decor has largely eroded away, including destroyed amber golems and chipped white and gold paint which has been stripped away to the obsidian base of the temple. Likely the good aligned wizards who built the temple originally were followers of Horus and the aesthetic was one mostly of white, gold, and amber, but all of the wizards were killed and the temple fell into ruin long before Strahd or Exethanter arrived.
Exethanter then would have found the temple which was now mostly obsidian and built his defenses to fit in with the temples. He summoned and bound the arcanaloth to protect the temple and built a large hollow statue for it to hide in. He also added two enchanted obsidian statues to collect souls for him to feed on. These statues may be based on no god or possibly some god that Exethanter follows, such as Vecna.
My personal thought is that Vecna is the escaped vestige who cursed the nothics as nothics are really the only reference to him in the whole module. The mourning glory is not the one to escape from that amber sarcophagus they escaped from a different one in the hidden level of the Amber Temple where all of the Adventurers League module takes place.