The atheist is claiming that anything that ends in survival of a sentient creature or its species is "good". While the theist is claiming that "good" is independent of survival of sentient creatures (though the two often run parallel). The atheist is making a claim that is teleological (purpose-based) while the theist is making a claim that is metaphysical (morally-based). When the two make the claim that their worldviews can support "objective" morality, understand that they do mean two totally different things. A consequence of this is that when a theist shows that atheism does not allow for a metaphysically moral good, the atheist is not really disagreeing with them, because atheism, by definition does not have a standard to base a metaphysically moral "good" on. However the atheist will still maintain that they can accommodate "objective good" because they maintain that certain actions are objectively good and bad for reaching a certain goal (survival, in this case), but again, they are talking about a different kind of "good".
I hope everyone read Luke's article!
Faithful Thinkers: Morality, Knowledge, and X-Men