ker boom

I think it was a alchemist

Okay then... am i the only one who found loot boxes there...

Yeah, when it happened to me the entire shack was burnt down and there's nothing loot able in it.

I was walking on top of it, when the prompt came up and quickly disappeared,

Good thing eagle eye is a thing...

Forgot what i stole tho, but there was 2 boxes i think

It under some wood near the perimeter of the destroyed wood

Im a little late but yes the official guide states that it was an Alchemists house

You can find buckshot incendiary shotgun shells pamphlet in a lockbox near the burning building.