Yes, pretty much that, it's even mentioned in the novels (not specifically by the Blood Knights, but by that rogue that tried to kill Malfurion). That, and the fact of the HE exile by the NE when they didn't wish to give up Arcane. And after seeing Suramar, would you blame them for not willing to give up that kind of lifestyle for sitting in the trees just because their new self proclaimed leadership decided to outlaw Arcane magic, as they believed it will always draw demons to them (which technically wasn''t true, as we now know why Burning Legion invaded Azeroth and that it had nothing to do with the Night Elves or even the Well of Eternity, but Sargeras' obsession with the World Soul).
And please stop putting XXI Century real life morality into the fantasy game setting and acting as if Burning of Teldrassil was some act of untold evil and not just typical war effort gone wrong. Obviously it was evil and wrong, but I don't think much of the Horde forces would bother with killing civilians during war time, when neither of sides cared about refraining from such actions. The problem with the Burning is incoherent story telling by Blizzard which sometimes portrays characters and their actions as if it was a PG-18 game setting with complex, multidimensional dilemmas and sometimes as if it was a Carebear island PG-3 with 2D simplistic stuff and dualistic Sylvanas - bad, Goldenhaired boy - Good.