I haven’t seen a Pyromancer video… but alot of people were guessing that. It was one of the more popular theories. It makes more sense than a direct assault from Denathrius.
I posted a theory a while back that ended up close to the mark :
I am just glad Blizzard is answering something, instead of leaving it out there for people to guess.
If you read that thread I posted in, in GD, it seems GD was 90% sure it was Denathrius himself, and not Argus, and that the question had already been answered. But I wasn’t as certain.