Because Johns is working in close conjunction with Tomasi, the guy who wrote that NIGHTWING storyt and could therefore actually say, "Hey, this is what I did in NIGHTWING with those bodies!"
Not foreshadowing, necessarily, but laying the groundwork. That's more what I meant. THE BLACKEST NIGHT has been in the works for two, three years, and Tomasi took over writing NIGHTWING, what, a year or two ago? Around the same time he took over GLC? You think he wouldn't have the GL plans in mind at the same time he wrote that in NIGHTWING?