auras are definitely not an attack of any kind. They're aura's. The monster manual glossary will tell you every thing you need to know about them, and it doesn't mention them being an attack.
Flaming sphere's auto-damage is aura like. And its NOT an attack, because it isn't called one. The sphere DOES have an attack, which it calls quite clearly an attack.
Some utilities can blur the line between attack and not attack (they often throw around the word "ranged" "close burst" etc), thats a different topic, but for the most part its only an attack if you see the word "attack" and its definitely only area/close if it says those words. Auras and flaming spheres do not, so there is not reason to think that they might be.
I see why you might wonder, and why its worth asking, but i'm pretty positive the answer is no. They are something different