At the end of the prior episode, we see the current Green Arrow as of 2046, and in this episode, we are introduced to his secret identity as Connor Hawke. Later on in the episode, he goes to talk to Oliver and it is revealed that Connor Hawke is actually John Diggle, Jr. This episode aired a full 8 months before Flash revealed that John's daughter Sara was now a son named John due to the Flashpoint Paradox.
This week's episode of Arrow, "Brothers & Sisters," appears to have a continuity error. Dinah seems surprised to find out that Connor Hawke is John's son. The writers could have easily had him clarify that he is John, Jr., and that she hadn't seen him since he was a child and before he started using an alias. Instead, they have Connor Hawke declare that John Diggle was his adoptive father.