A link between eras.

Demons are simply an ancient name, I think. Old myths resurfaced in people's memories, and that's why they were called that. Hey, what an idea!:D

Krigans cannot be demons. Let me explain. The answer lies in physiology.
Krigans are essentially parasites (see the sci-fi movie "Independence Day"). Their goal is the destruction of all living things and pumping resources out of the planet. Conquest doesn't interest them in principle. Krigan Guide MM6.
Inferno.
1. They cannot live in the world of humans!!!!!!!!!!(Read the castle description)
2. They don't need the world of humans, neither for resources nor as living space.
3. It's generally unclear why they attacked?????????
4. The atmosphere of Ashan doesn't suit them. Due to the low temperature;)

in general, do not confuse them.