I'm assuming (but might be wrong) that he's referring to this;
So, Now Richard Dawkins Is Pondering the Ethics of Cannibalism and ‘Human Steak’ | RELEVANT
Now...2 key points...
1) Dawkins doesn't get to speak for atheists in general, and frankly this was a weird tangent from him for the original topic anyway.
2) He was talking about cultured meat (basically being able to grow meat rather than kill animals). Doesn't make his point any less strange, really, but he wasn't talking about killing and eating people.
That's my best guess what the OP was on about. If he posted about Dawkins, specifically, the topic would make more sense (but still be a bit of a misrepresentation).
If that's not what he's referring to, I remain lost!!