So... What is the source of Fiddlesticks' resurrection exactly?

In Fiddlesticks' new lore, he is described as once having been a lonely farmer that was blamed for the famine on his village and was left to starve in his own barren field.

However.

The crows who came to feast on his corpse somehow managed to "resurrect" him for some unknown reason.

He then somehow became the scarecrow he is now, his entire body seemingly just replaced with the wooden sticks he uses as a pseudo skeleton now, and managed to get control over the crows (alternatively, the crows might be controlling him).

In the short story To Our End, his eyes are described to be glowing with green Wychfire. However, I cannot seem to find a definition to what Wychfire is.

So here is my question(s) for the day:

Who are these crows? How did they get the power to resurrect him? Could Swain perhaps be involved?

(All information is taken from the official League of Legends website: https://universe.leagueoflegends.com/en_US/champion/fiddlesticks/)