Reading that the Horde burn down Teldrassil, that seems very, very out of character for the Horde. It seems like the druids on the Horde side would step in and say something.
My guess is that someone on the Horde side does this w/o meaning besides starting a war, similar to they reason the Horde retreated at the broken shore, it was not a faction driven dilemma, it was a matter of life or death.
I may even go to the extent that Jaina did it to make the Horde and Alliance start going to war again.
TL;DR I am die hard Alliance, and even to me burning down Teldrassil seems so out of character for the Horde.