Alright, so in that example it is saying that a priestess is attacking the whirling spirit with her basic attack. The priestess' basic attack is 3 dice, but for simplicity's sake I'm going to go with what they said and she has gotten done rolling two of her attack dice, one being 1 damage, the other being 2 damage. Because the whirling spirit is incorporeal, only the 1 counts for damage and the 2 counts as a 0.
It then goes on to say that if those two dice were from pillar of light (which would in fact roll 4 dice because of it doing +2 against non-living) both the 2 and the 1 would count because pillar of light has the ethereal trait. I agree that it's a bit awkward, it's just trying to convey the message that if an attack doesn't have ethereal only 1s count, and if it does, you do damage as normal.
As for whirling spirit, it rolls a 4 dice attack when attacking creatures. It has Ethereal, so attacks against Incorporeal objects do normal damage instead of just 1s counting. When attacking Incorporeal objects, it gets +2 attack dice, so if the object it is attacking is also incorporeal, it rolls 6 attack dice instead of 4.
As an added bonus, because the +2 vs. Incorporeal is modifying dice against a trait, you would also get +2 on the effect die as well for the push.