No. The current wording on Kael'thas's Flamestrike says it's not an attack.
OCR:Kael'thas's Flamestrike, T2R2, Prince Kael'thas Sunstrider
Fire
Prince Kael'thas Sunstrider Only
Place a flame counter in target space within range. <p> At the start of Kael'thas's next turn, he makes a [M8] (Fire) attack against all enemies on or adjacent to that counter.
[Crit]: Damage +1. (Remove that counter after the attack or as Kael'thas leaves play.)
Cheers!
-teh Sig
Level 2 Minis Judge.