Three panels after reminding us that Damian is Bruce's son, a long-time family friend introduces Dick, who he knows to be Bruce's son (one of several) as NOT Bruce's son.
I also would like an explanation. I think it's because Morrison is so enamored with his original character that now genetics tops earlier relationships and Batverse history. I hope I'm wrong, but in every issue of Batman and Robin we've been told that Damian is the "true" son. And Dick, Jason and Tim (all legally adopted--Cass's is also mentioned as pending in one issue of that last BG series) are all just placeholders for the true son.