Surviving a fire unharmed, giving birth to anthropomorphic black clouds that assassinate people, and reviving the dead are all pretty much magic -- unless you invoke advanced nanotechnology perhaps. The bizarre flora and fauna I'll attribute to genetic engineering.
The Valyrians were purported to have had advanced technology now lost to the world.
The opening graphics of the TV series make the world appear to be an orbital or a segment of a shell-type Dyson sphere, and the sun to be artificial. Anyway, we've seen the "sun" rising and setting so that makes that theory problematic. I'll discount that.
The characters talk about Winters lasting years, so a very elliptical orbit wouldn't fit the bill. The simplest explanation would be for the sun to be an irregular variable star.